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INDICES OF STOCK STATUS OBTAINED FROM THE CANADIAN BLUEFIN TUNA FISHERY

by

J.D. Neilson1, S. Smith1, M. Ortiz2, and B. Lester3

SUMMARY Updated standardized relative abundance indices are presented for Canadian

bluefin tuna fisheries in the Gulf of St. Lawrence (1981-2007) and off Southwest Nova Scotia (1988-2007) based on data from commercial log records. Methods used were as in the 2006 bluefin tuna stock assessment. A step-wise regression was used to determine the most appropriate delta lognormal-binomial model specifications for standardizing both CPUE series. CPUEs in the Gulf of St Lawrence have increased slightly from 1997 to 2003, rapidly increased in 2004 and have remained high. The catch rates in 2007 are the highest in the time series, almost the 3x the series average. The Southwest Nova Scotia series has had a fairly stable trend through the mid- to late 1990s. While 2000 is the lowest value on record, catch rates have been following a slightly increasing trend since then. The 2007 catch rates are close (0.98) to the series average.

The spatial distribution of the Canadian fisheries has not changed significantly,

but there were anecdotal reports of tuna occurring in areas where they have not been observed in many years (for example, the Baie des Chaleurs in the western Gulf of St. Lawrence). The size composition of the catch in the southern Gulf of St. Lawrence over the past 5-6 years has generally followed a declining trend that has recently stabilized, and is now increasing. The condition (Fulton’s K) of individual fish in the southern Gulf of St. Lawrence has been following a declining trend and is now at the lowest value in the series.

KEYWORDS: tuna fisheries catch rates, size composition

1 Fisheries & Oceans Canada, Biological Station, 531 Brandy Cove Road, St. Andrews, NB E5B 2L9 CANADA. Email address of lead author: neilsonj@mar.dfo-mpo.gc.ca. 2 U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Marine Fisheries Service, 75

Virginia Beach Drive, Miami, Florida, 33149 U.S.A. 3 Fisheries & Oceans Canada,

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1.0 INTRODUCTION This paper presents a synopsis of recent developments, catch composition and catch rates in the bluefin tuna fishery conducted by Canada. The catch rate information updates standardized Canadian series for bluefin tuna fisheries in the Gulf of St. Lawrence (age 13+) and off Southwest Nova Scotia (ages 7-13) presented in Neilson et al. (2007). Those authors used a step-wise regression to determine the most appropriate delta lognormal-binomial catch rate model, and the series were used in the 2006 stock assessment (Anon 2007). In the current paper, a similar approach was employed to update the information as potential indices of abundance for the 2008 stock assessment.

2.0 DESCRIPTION OF THE FISHERIES, LOCATIONS FISHED, AND LANDINGS Canadian bluefin tuna fisheries currently operate in several geographic areas off the Atlantic coast from July to November, when bluefin tuna have migrated into Canadian waters (Fig. 1). The main commercial fisheries occur off the coast of Nova Scotia (Hell Hole rod and reel/tended line, Bay of Fundy harpoon, St. Margaret’s Bay trap, Canso rod and reel, and Halifax rod and reel/tended line), in the southern Gulf of St. Lawrence (tended line/rod and reel) and sporadically along western edge and central region of the Grand Banks (tended line/rod and reel). The rod and reel fishery in the southern Gulf of St. Lawrence in 2007 had a similar spatial distribution to that observed in 2005 and 2006 (Fig. 2). The fishery typically is conducted in waters north of Prince Edward Island and west of Cape Breton Island. The tended line, rod and reel and electric harpoon fishery off south-west Nova Scotia also showed general consistency in the areas fished (Fig. 3) from 2005 to 2007. Catches were localized off the northern edge of Georges Bank, the Hell Hole (mouth of the Fundian Channel) and several coastal locations off Nova Scotia. The mouth of the Bay of Fundy usually is a ‘hotspot’, but not in 2005. The pelagic longline fishery, which targets multiple large pelagics species, usually is often associated closely with the edge of the Scotian Shelf (see, for example, 2005 (Fig. 4), moved further offshore to target tropical tunas and to avoid excessive catches of swordfish, which were abundant in 2006 and 2007. The distribution of the tended line and rod and reel fishery off southern Newfoundland has not changed appreciably in recent years (Fig. 5)

Annual landings and Canadian quotas are shown in Fig. 6. The fishery has generally caught close to the available quota, particularly during the competitive fishery period (prior to 2004). A new management approach was implemented for the 2004 fishing season, which resulted in individual fleet sectors being assigned a specific share of the Canadian quota based on catch history. Fleets operate independently of each other, adopting their own strategies to address when and how to harvest the resource (Calcutt et al. 2005). The performance of each fleet sector in relation to the assigned quota is shown in Fig. 7. As noted later in Section 9.0, industry has noted that fleet shortfalls in 2007 were related more to market considerations and their decision to carryover their allocations within the management period. 3.0 TRENDS IN FISHING CAPACITY The number of license holders eligible to land bluefin tuna was 776 from 1999 - 2003, and increased to 777 in 2004 and has remained constant since then. The number of vessels active in the fishery has varied from year to year, and is shown in Fig. 8, by fleet sector and gear type. In the Gulf of St. Lawrence, the dominant gear type is rod and reel, and the tended line component has become less significant. In the Southwest Nova Scotia fishery, rod and reel is also dominant followed by the tended line fishery.

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4.0 DATA COLLECTION SYSTEMS In Canada, submission of log records for the bluefin tuna fishery was initially done on a voluntary basis, although since 1994 it has been mandatory. While log record coverage has varied over the years, it has been assumed that what is available is representative of the fishery. The Canadian Atlantic statistical systems provide real time monitoring of catch and effort for all fishing trips. Since 1996, this system has applied to all fleets and included monitoring of all trips even when no fish were caught. At the completion of each fishing trip, independent and certified Dockside Monitors must be present for off-loading, and log record data must be submitted by each fisherman to the Monitoring Company that inputs the data into a central computer system. The computerized log records provide detailed information on catch (number and weight of tuna), size (individual weight and length), effort (hours fished), date, gear characteristics, home port (fleet) and catch location (latitude and longitude). Ideally, this ensures 100% coverage of properly completed log records and individual fish sizes. In actuality, 94% of individual bluefin landed in 2007 had associated size information. 5.0 TRENDS IN SIZE COMPOSITION In the southern Gulf of St. Lawrence rod and reel fishery, the median weight of the catch has declined since 2000, accompanied by an increase in the range of weights caught in that fishery (Fig. 9). There is evidence that the decline in the median round weight stopped in 2005, and the medians have increased in the past two years. In the Southwest Nova Scotia rod and reel fishery, the median round weight of the fish has declined from 1996 to 2002 and followed an increasing trend to 2005. The 2005 fishery, as seen in Fig. 9, had more activity on the northern edge of Georges Bank, an area associated with fish of larger size compared with those caught in other areas off Southwest Nova Scotia, according to the fishing industry (see also Section 9.0, Commentary From the Fishing Industry). Length-frequency information for the Gulf of St. Lawrence rod and reel fishery is shown in Fig. 10. The length composition information reflects the trends in median weight described above, in general. In 1999-2000 there was a greater proportion of the catch in the 300+ cm length classes. However, the modal lengths in the catch have increased from 2002 to the present. The ages (from the Turner and Restrepo (1994) growth model) represented in the catch are generally from ages 10 to 20. 6.0. CONDITION OF THE CATCH We calculated the trend in condition (Fulton’s K, ((W/L3)*100,000)), after standardizing for effects of length class, month and year (Fig. 11). The condition of bluefin tuna caught in 2007 was the lowest in the available series. The observation of declining condition has also been made elsewhere in the range of western bluefin tuna. Recent examination of 14 years of records from a New Hampshire fish auction house provided by a single experienced tuna buyer indicate a trend towards lower oil content and slimmer body shape since 1991 (Goulet et al. 2007), but the declining trend is not concurrent with that observed in the southern Gulf of St. Lawrence (having started earlier). 7.0 CATCH RATE SERIES As completed by Neilson et al. 2007, two separate standardized indices were developed based on (1) the spatial distribution of catches, (2) differences in the size of fish captured, and (3) patterns of nominal CPUE: Gulf of St. Lawrence tended line/rod and reel (1981-2005), and Southwest Nova Scotia tended line/harpoon/rod and reel (=Hell Hole plus Bay of Fundy, 1988-2005). Based on the von Bertalanffy

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growth parameters calculated by Turner and Restrepo (1994), the Southwest Nova Scotia fisheries capture bluefin tuna aged 7-13 and the Gulf of St. Lawrence fishery captures bluefin tuna aged 13+. These two series encompass the overall size/age range of tuna captured in the Canadian fishery and represent about 80% of the Canadian landings. 7.1 Catch and effort data Logbook data were edited and condensed to the trip level to provide total number of fish and total number of hours fished per trip by area, fleet, month and gear type. Catch per hour was the unit measure of effort selected for all fisheries used in the standardized series. This measure is most appropriate when effective fishing time during a day is generally limited to a period of time influenced by the tidal cycle and when trips occur over more than one day. Standardized CPUE was calculated as the number of tuna captured per trip divided by total hours fished per trip. For the delta model formulations, the nominal CPUE for both the Gulf of St Lawrence and Southwest Nova Scotia was scaled by a factor of 100. 7.1.1 Gulf of St. Lawrence Series The Gulf of St. Lawrence standardized index was based on catch and effort data for vessels with 10+ trips per year and included observations for 27 years (1981-2007), three months (August, September, October), two fleets (Prince Edward Island and Gulf Nova Scotia) and two gear types (tended line, rod and reel) (n= 77553 trips). The 10+ trip threshold restricts the analysis to full time, experienced fishermen that fish the main months of the fishery (August-October). Trips with CPUE=0 were included in the series and represented over 90% of the observations, therefore, the data used in these analyses are binomially distributed, with catch observations of zero or one (Fig. 12; Stone et al. 2001). 7.1.2 Southwest Nova Scotia Series Catch and effort data aggregated by trip from the Hell Hole (1988-2007) and Bay of Fundy (1992-2007) areas were combined and used in the development of a standardized CPUE series for Southwest Nova Scotia (see Stone et al. 2001). Catch data for this series essentially followed a Poisson distribution; trips with catch=0 were included in the series and represented 26% of the observations while the remaining 74% consisted of trips with catches ranging from 1 to 22 fish (Fig. 7). The data set used for CPUE standardization included observations for 20 years (1988-2007), two areas (Hell Hole, Bay of Fundy), five fleet sectors (Nova Scotia, Prince Edward Island, Quebec, Gulf Nova Scotia, Gulf New Brunswick), three gear types (rod and reel, tended line, harpoon), and three months (August, September, October) (n=5342 trips). Recently, the use of rod and reel gear has become increasingly popular (Stone et al. 2001). 8.2 Models and specifications Consistent with the approach recommended by Porter et al. (2003) and Neilson et al (2007), we used step-wise regression to determine the set of systematic factors and interactions that significantly explained the observed variability (Tables 1 and 2). The difference of deviance between two consecutive models follows a χ2 (Chi-square) distribution. This statistic was used to test for the significance of an additional factor in the model. The number of additional parameters associated with the added factor minus one corresponds to the number of degrees of freedom in the χ2 test (McCullagh and Nelder, 1989 pp 393). Final selection of explanatory factors was conditional on: a) the relative percent of deviance explained by adding the factor in evaluation (normally factors that explained more than 5% were selected), b) the χ2

test significance, and c) the Type III test significance within the final specified model.

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Once a set of fixed factors was specified, possible interactions were evaluated, in particular interactions between the year effect and other factors. Selection of the final mixed model was based on the Akaike’s Information Criterion (AIC), the Schwarz’s Bayesian Criterion (SBC), and a chi-square test of the difference between the –2 log-likelihood statistic of a successive model formulation (Littell et al. 1996) (Table 2). Relative indices for the delta model formulation were calculated as the product of the year effect least square means (LSMeans) from the binomial and the lognormal model components. The LSMeans estimates use a weighted factor of the proportional observed margins in the input data to account for the non-balance characteristics of the data. LSMeans of lognormal positive trips were bias corrected using Lo et al. (1992) algorithms. Analyses were done using the GLIMMIX and MIXED procedures from the SAS® statistical computer software (SAS Institute Inc. 1997).

For the Gulf of St. Lawrence standardized series, the final models that were combined using the delta-binomial method with random effects to produce a single index that included the following variables (see Table 3 and Fig. 13 for diagnostic plots):

Proportion positive: Fixed effects: year fleet month gear Random effects: year*month year*gear

Positive catch rates:

Fixed effects: year gear fleet Random effects: * fleet year*month

For the Southwest Nova Scotia standardized series, the final models that were combined using the delta-binomial method with random effects to produce a single index included the following variables (see Fig. 13 for diagnostic plots):

Proportion positive: Fixed effects: year month area fleet Random effects: year*area year*month year*fleet

Positive catch rates:

Fixed effects: Year Month area gear fleet Random effects: year*month year*fleet year*gear

8.3 CPUE Standardization – Results CPUEs in the Gulf of St Lawrence have increased slightly from 1997 to 2003, rapidly increased in 2004 and have remained high (Fig. 14). The catch rates in 2007 are the highest in the time series, almost the 3x the series average (Table 4). The Southwest Nova Scotia series has had a fairly stable trend through the mid- to late 1990s (Fig. 15). While 2000 is the lowest value on record, catch rates have been following a slightly increasing trend since then. The 2007 catch rates are close (0.98) to the series average.

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The standardized series for both the Gulf of St. Lawrence and Southwest Nova Scotia follow the nominal series closely (Tables 4, 5; Figs. 14, 15). Porter et al. (2003) also noted that for both the Gulf of St. Lawrence and the Southwest Nova Scotia fisheries, the standardized CPUE series seem to track each other well over the period of 1995 to 2001, and given such apparent synchrony, suggested an extrinsic factor influencing abundance. Any synchrony is now less apparent since 2001, as the catch rate series for the Gulf of St. Lawrence has increased considerably faster than that of the fishery off Southwest Nova Scotia. 9.0 COMMENTARY FROM FISHING INDUSTRY Industry consultations occurred in Dartmouth, Nova Scotia (May 27th, 2008) and Charlottetown, Prince Edward Island (June 3rd, 2008). These meetings were well-attended by those with an interest in the fisheries, and considerable useful feedback on the fisheries was obtained. Fishery Distribution Considering the distribution of the fishery, industry representatives generally agreed with DFO Science’s view that the traditional bluefin tuna fishing areas have not changed in recent years. However, they also noted that tuna were observed in 2007 in areas where they have been absent recently, but have supported tuna fisheries historically. In particular, anecdotal reports were received from herring fishermen of bluefin tuna occurring in the western Gulf of St. Lawrence, including the Baie des Chaleurs. Fuel costs were mentioned as a factor that will shape the fishery distribution information in the near future. For example, fishing in the lower Bay of Fundy takes more fuel for the southwest Nova Scotia fleet compared with the Georges Bank fishery. Catch Rates and Fishery Performance Discussions concerning fishery catch rates indicated that industry had no difficulty encountering fish. On the contrary, exceptional catch rates were noted in the southern Gulf of St. Lawrence. The sectors operating there are considering measures such as a one fish limit per trip to help extend the fishing season. During discussions in Charlottetown, the exceptional fishing season in 2007 was reviewed. Participants noted that contrary to previous years where high catch rates were observed only in the eastern or western part of the southern Gulf, good catch rates were wide-spread. While there were a few sectors that did not catch their 2007 quota, this was due to fishermen opting not to fish due to poor market conditions, with the possibility of quota carry-forward to 2008, the end of the current management period. Industry also noted that changes in the management regime (such as the move to fleet quotas in 2004) and ex-sector fishing can influence the overall catch rates. It was noted that the large jump in catch rates in the southern Gulf of St. Lawrence fishery coincided with the introduction of fleet quotas. However, it is difficult to imagine a mechanism for the rapid increase in CPUE related to this change, which is intended to spread fishing effort out over the season. However, with the very high catch rates experienced in the Gulf of St. Lawrence fishery recently, this objective has not been fully met. Size Composition

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Concerning trends in the size of the fish caught in Canadian fisheries, industry stressed that to some extent, and the size of fish landed reflects market demand. Fish of certain size are known to congregate in certain locations (for example, smaller fish are found in the Hell Hole), which fishermen target depending on market conditions. Most recently, southwest Nova Scotia fishermen have been avoiding areas where larger fish are known to occur. Gulf fishermen noted that larger fish often enter the southern Gulf later in the season. With the current seasons being shorter than in the past, this may be an explanation for the trend towards smaller fish in the landings. Fishermen also expressed the view that larger fish do not co-occur with smaller tuna, and the former fish will vacate when schools of small fish move into an area. Concerning the downward trend of condition of bluefin tuna, the size of the fish is a more important market consideration. It was noted that observations of small (30-50 kg) bluefin tuna were common on the Scotian Shelf in 2007. These anecdotal reports are supported by reports from fishery observers. A summary of the views obtained during the two consultations is given in Table 5. 10. CONCLUSIONS AND RECOMMENDATIONS

The two abundance series for the Canadian fisheries presented here are following increasing trends, most notably for the southern Gulf of St. Lawrence. The CPUE series presented here as indices of abundance have some caveats, as do all such series. While fishermen generally agree that the abundance of fish has increased in the past four years, it is recognized that there are factors affecting the operation of the fishery that are not currently considered in this analyses (ie. changes in gear, changes in management approach, and a recent cooling trend in the southern Gulf). The impacts of such factors on the catch rate series remain sources of uncertainty in the current analysis, and could be profitable areas for further research. The consequences of the observation that fish are in lower condition during their late summer residence in the Gulf of St. Lawrence on subsequent reproduction and survival are unknown at present. However, in other marine fish stocks such as Atlantic cod (Gadus morhua), there is evidence that a population of fish in relatively poor condition could show lower productivity, manifested by lower fecundity (Kjesbu et al. 1998), or higher post-spawning mortality (Dutil and Lambert 2000). Therefore, the trend of declining bluefin tuna condition should be considered a negative signal with potentially harmful consequences to the population. In addition, the implications of lower average weight for a given length/age may have implications for the projections. To give some appreciation of the possible scale of this bias, the SCRS examined the impact of using alternate weights at age in the 2006 assessment and concluded that the discrepancy observed in 2005 was not likely to result in a major (>10%) difference in population parameters such as SSB. This bias, while likely small, still persists in the length and weight data from the southern Gulf of St. Lawrence, based on observed trends in condition. 11. LITERATURE CITED

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ANON. 2007. Report of the 2006 ICCAT SCRS bluefin tuna stock assessment session. Col. Vol. Sci.

Pap. ICCAT, 60(3): 652-880. CALCUTT, M., S. Paul, J. Neilson, and A. McMaster. 2005. National Report of Canada, 2004. Int.

Comm. Conserv. Atl. Tunas ANN-006/2005. DUTIL, J.D. and Y. Lambert. 2000. Natural mortality from poor condition in Atlantic cod (Gadus

morhua). Canadian Journal of Fisheries and Aquatic Sciences. 57(4): 826-836. GOLET, A. Cooper, R. Campbell and M. Lutcavage. 2007. Decline in condition factor of Atlantic

bluefin tuna (Thunnus thynnus) in the Gulf of Maine. Fish. Bull. 105:390–395

KJESBU, O.S., P.R. Whitthames, P. Solemdal and M. Greer Walker. 1998. Temporal variations in the fecundity of Arcto-Norwegian cod (Gadus morhua) in response to natural changes in food and temperature. Journal of Sea Research 40, 303-321.

LITTELL, R.C., G.A. Milliken, W.W. Stroup, and R.D Wolfinger. 1996. SAS® System for Mixed

Models, Cary NC:SAS Institute Inc., 1996. 663 pp. LO, N.C., L.D. Jacobson, and J.L. Squire. 1992. Indices of relative abundance from fish spotter data

based on delta-lognormal models. Can. J. Fish. Aquat. Sci. 49; 2515-2526. MCCULLAGH, P. and J.A. Nelder. 1989. Generalized Linear Models 2nd edition. Chapman & Hall. NEILSON, J.D. Paul, S.D. and M. Ortiz. 2007. Indices of stock status obtained from the Canadian

bluefin tuna fishery. Col. Vol. Sci. Pap. ICCAT, 60(3): 976-1000. PORTER, J.M., M. Ortiz and S.D. Paul. 2003. Updated standardized CPUE indices for Canadian bluefin

tuna fisheries based on commercial catch rates. Col. Vol. Sci. Pap. ICCAT, 55(3): 1005-1018. SAS INSTITUTE INC. 1997, SAS/STAT® Software: Changes and Enhancements through Release 6.12.

Cary, NC:Sas Institute Inc., 1997. 1167 pp. STONE, H.H., M. Ortiz, and J.M. Porter. 2001. Updated standardized CPUE indices for Canadian bluefin

tuna fisheries. Int. Comm. Conserv. Atl. Tunas, Coll. Vol. Sci. Pap., Madrid 52: 959-976. TURNER, S.C., and V.R. Restrepo. 1994. A review of the growth rate of west Atlantic bluefin tuna,

Thunnus thynnus, estimated from marked and recaptured fish. SCRS/1993/065.

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Table 1. Summary of step-wise regression analyses used for determining the most appropriate delta lognormal-binomial model specifications for standardizing CPUE series from the Gulf of St. Lawrence. The table includes the deviance for the proportion of positive observations (i.e. positive trips/total trips) and the deviance for the positive catch rates. Shaded areas indicate factors selected for model formulations.

Bluefin tuna 2008 Gulf of St Lawrence factor analysis/ Deviance table

Model factors positive catch rates valuesDegrees of

freedomResidual deviance

Change in deviance

% of total deviance p

1 1 3117.4Year 26 3040.6 76.8 56.6% < 0.001Year Month 2 3039.3 1.4 1.0% 0.506Year Month Gear 1 3036.7 2.6 1.9% 0.108Year Month Gear Fleet 1 3014.3 22.4 16.5% < 0.001Year Month Gear Fleet Month*Fleet 2 3014.1 0.2 0.1% 0.916Year Month Gear Fleet Month*Gearc 2 3008.3 6.0 4.4% 0.051Year Month Gear Fleet Year*Gearc 16 3008.1 6.2 4.6% 0.986Year Month Gear Fleet Gearc*Fleet 1 3007.7 6.6 4.9% 0.010Year Month Gear Fleet Year*Fleet 18 2996.7 17.6 13.0% 0.481Year Month Gear Fleet Year*Month 44 2981.8 32.5 24.0% 0.900

Model factors proportion positivesDegrees of

freedomResidual deviance

Change in deviance

% of total deviance p

1 1 3063.4Year 26 1125.2 1938.22 73.2% < 0.001Year Month 2 1104.2 21.02 0.8% < 0.001Year Month Fleet 1 853.5 250.63 9.5% < 0.001Year Month Fleet Gearc 1 780.8 72.77 2.7% < 0.001Year Month Fleet Gearc Month*Fleet 2 762.0 18.76 0.7% < 0.001Year Month Fleet Gearc Month*Gearc 2 741.4 39.42 1.5% < 0.001Year Month Fleet Gearc Fleet*Gearc 1 739.6 41.19 1.6% < 0.001Year Month Fleet Gearc Year*Fleet 20 686.1 94.71 3.6% < 0.001Year Month Fleet Gearc Year*Gearc 20 648.2 132.56 5.0% < 0.001Year Month Fleet Gearc Year*Month 48 416.9 363.88 13.7% < 0.001

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Table 2. Summary of step-wise regression analyses used for determining the most appropriate delta lognormal-binomial

model specifications for standardizing CPUE series for Southwest Nova Scotia. The table includes the deviance for the proportion of positive observations (i.e. positive trips/total trips) and the deviance for the positive catch rates. Shaded areas indicate factors selected for model formulations.

Model factors positive catch rates values d.f.Residual deviance

Change in deviance

% of total deviance p

1 1 3775.0Year 19 2839.4 935.6 84.5% < 0.001Year Month 2 2835.2 4.1 0.4% 0.127Year Month Area 1 2833.4 1.8 0.2% 0.179Year Month Area Gear 1 2829.1 4.3 0.4% 0.037Year Month Area Gear Fleet 4 2815.5 13.6 1.2% 0.009Year Month Area Gear Fleet Area*Fleet 3 2814.5 0.9 0.1% 0.820Year Month Area Gear Fleet Month*Area 2 2810.7 4.8 0.4% 0.092Year Month Area Gear Fleet Month*Fleet 8 2800.7 14.8 1.3% 0.063Year Month Area Gear Fleet Month*Gear 4 2780.8 34.6 3.1% < 0.001Year Month Area Gear Fleet Year*Area 15 2750.8 64.7 5.8% < 0.001Year Month Area Gear Fleet Year*Gear 26 2735.5 80.0 7.2% < 0.001Year Month Area Gear Fleet Year*Month 36 2679.2 136.3 12.3% < 0.001Year Month Area Gear Fleet Year*Fleet 70 2667.2 148.3 13.4% < 0.001

Model factors proportion positives d.f.Residual deviance

Change in deviance

% of total deviance p

1 1 2530.8Year 19 1394.5 1136.34 57.3% < 0.001Year Month 2 1195.3 199.17 10.1% < 0.001Year Month Area 1 1088.4 106.88 5.4% < 0.001Year Month Area Gear 1 1074.0 14.44 0.7% < 0.001Year Month Area Gear Fleet 4 912.0 162.00 8.2% < 0.001Year Month Area Gear Area*Fleet 3 899.3 12.70 0.6% 0.005Year Month Area Gear Gear*Fleet 7 826.2 85.83 4.3% < 0.001Year Month Area Gear Year*Area 15 810.1 101.86 5.1% < 0.001Year Month Area Gear Year*Month 36 780.2 131.84 6.7% < 0.001Year Month Area Gear Year*Gear 26 774.6 137.42 6.9% < 0.001Year Month Area Gear Year*Fleet 71 549.3 362.68 18.3% < 0.001

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Table 3. Selection criteria for delta lognormal-binomial mixed models used for the standardization of the

a) Gulf of St. Lawrence and b) Southwest Nova Scotia catch rate series. Models with asterisks were chosen for CPUE standardization.

Canada Bluefin tuna

Gulf St Lawrence Model -2 REM Log likelihood

Akaike's Information

Criterion

Schwartz's Bayesian Criterion

Proportion Positives Year Fleet Month Gear 609.3 611.3 614.5Year Fleet Month Gear Year*Month 582.8 586.6 591.5 26.5 0.0000

*** Year Fleet Month Gear Year*Month Year*Gear 558.3 564.4 571.3 24.5 0.0000Year Fleet Month Gear Year*Month Year*Gear Year*Fleet 558.3 564.3 571.3 0 N/A

Positive CatchYear Fleet Gear 13552.6 13554.6 13561.4Year Fleet Month Year*Fleet 13548 13552 13555.7 4.6 0.0320

*** Year Fleet Month Year*Fleet Year*Month 13540.3 13546.3 13551.8 7.7 0.0055

Southwest Nova Scotia -2 REM Log likelihood

Akaike's Information

Criterion

Schwartz's Bayesian Criterion

Proportion Positives Year Month Area Fleet 1475.8 1477.8 1481.6Year Month Area Fleet Year*Area 1472.2 1476.2 1479.4 3.6 0.0578Year Month Area Fleet Year*Area Year*Month 1457 1463 1467.7 15.2 0.0001

*** Year Month Area Fleet Year*Area Year*Month Year*Fleet 1406.7 1414.7 1421 50.3 0.0000

Positive CatchYear Month Area Gear Fleet 10170 10172 10179.3Year Month Area Gear Fleet Year*Month 10068 10072 10076.1 102 5.552E-24Year Month Area Gear Fleet Year*Month Year*Fleet 9990.3 9996.3 10002.5 77.7 0.0000

*** Year Month Area Gear Fleet Year*Month Year*Fleet Year*Gear 9959.2 9967.2 9975.4 31.1 0.0000

Likelihood Ratio Test

Likelihood Ratio Test

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Table 4. Nominal and standardized (delta lognormal-binomial mixed model) CPUE series (tuna/100 hours) for the

Canadian bluefin tuna tended line/rod and reel fishery in the Gulf of St. Lawrence based on catch and effort data from commercial log records for Prince Edward Island and Gulf Nova Scotia vessels with 10+ trips annually from August through October, 1981-2007. (Nominal CPUE= number of tuna per 100 hours of fishing). The index is scaled to the average of the time series.

Delta lgN CPUE

Year No of trips No fish

Hours fished Nominal Index SE CV

1981 1643 248 12348 1.952 1.834 0.775 0.423 1982 4122 303 28052 2.261 1.741 0.761 0.437 1983 4262 525 31268 3.368 2.660 1.091 0.410 1984 1362 152 11651 2.277 1.501 0.637 0.424 1985 1465 61 13186 0.661 0.567 0.289 0.511 1986 673 26 5775 0.870 0.727 0.396 0.544 1987 263 8 1615 0.456 0.425 0.328 0.772 1988 410 22 3276 0.945 0.803 0.473 0.589 1989 320 16 2821 0.978 0.806 0.507 0.629 1990 827 22 6335 0.592 0.458 0.267 0.583 1991 310 15 2075 0.975 0.804 0.499 0.620 1992 466 27 3123 1.129 0.872 0.474 0.543 1993 937 66 7806 1.130 0.970 0.394 0.407 1994 1494 39 12859 0.538 0.332 0.162 0.487 1995 2353 170 21906 1.633 1.176 0.422 0.359 1996 7018 213 56265 0.702 0.402 0.152 0.378 1997 6269 189 51176 0.750 0.398 0.154 0.386 1998 3954 224 33477 1.371 0.753 0.279 0.371 1999 3538 347 30817 2.120 1.078 0.395 0.366 2000 6543 506 58233 1.756 0.914 0.338 0.370 2001 5401 360 47603 1.722 1.016 0.393 0.386 2002 5663 495 51272 1.956 0.911 0.386 0.423 2003 4237 362 38811 1.848 1.277 0.519 0.406 2004 2672 444 24680 4.146 2.271 0.944 0.416 2005 4092 582 40990 3.131 2.023 0.764 0.378 2006 5619 784 54870 3.244 2.034 0.768 0.378 2007 1640 432 16485 5.280 2.934 1.062 0.362

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Table 5. Nominal and standardized CPUE series for combined Canadian bluefin tuna fisheries in the Southwest Nova

Scotia bluefin fishery (rod and reel/tended line, harpoon) based on catch and effort data from commercial log records for August through October, 1988-2007. The index is scaled to the mean of the time series.

Year N Obs Hours fished No fish Nominal Index SE CV

1988 40 845 230 42.98 2.10 0.15 0.501989 214 3158 1120 57.01 3.47 0.21 0.431990 166 2666 861 54.49 2.17 0.13 0.431991 218 3452 714 32.57 1.28 0.09 0.521992 232 4759 857 25.44 1.30 0.07 0.391993 651 11244 1039 12.77 0.35 0.03 0.541994 282 4992 867 24.76 1.22 0.07 0.391995 330 7534 1088 21.89 0.85 0.05 0.381996 373 10315 675 7.29 0.36 0.03 0.491997 366 9616 445 5.97 0.25 0.02 0.551998 350 8931 845 11.95 0.37 0.02 0.481999 266 5653 894 19.76 0.91 0.06 0.482000 280 7208 347 5.45 0.17 0.01 0.612001 359 9162 1027 13.33 0.62 0.04 0.422002 485 9084 1108 12.67 0.41 0.03 0.602003 187 5841 1094 26.82 1.11 0.06 0.392004 152 6420 562 12.82 0.49 0.03 0.492005 156 5811 595 16.18 0.59 0.04 0.512006 142 5979 727 16.31 1.02 0.05 0.382007 93 3632 347 16.27 0.98 0.05 0.38

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Table 6. Suimmary of views obtained during consultations with the bluefin fishing industry prior to the 2008 stock assessment.

Positive Indicators Negative Indicators

Both indices of abundance have followed an increasing (Gulf) or stable (SWNS) trend since the last assessment. Fleets indicate no problems with abundance of fish.

Condition of the fish in the Gulf of St. Lawrence has been declining (significance of this is unclear).

All traditional fishing areas remain productive. In addition, in some areas where tuna have not been seen in many years, there are anecdotal reports of tuna occurrences (western Gulf of St. Lawrence, Baie de Chaleurs).

The trend of smaller average size of tuna in the Gulf of St. Lawrence fishery has reversed in the last two years.

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Figure 1. Canadian Atlantic Zone, showing geographic location of provinces (bold), major fishing

locations and the transboundary border between Canada and the USA (solid line).

70° 68° 66° 64° 62° 60° 58° 56° 54° 52° 50° 48°40°

41°

42°

43°

44°

45°

46°

47°

48°

49°

50°

51°

Georges Bank

USA Bay of Fundy

St. Margarets BayHalifax

CansoCape Breton Island

Hell Hole

New Brunswick

Nova Scotia

P.E.I.

Newfoundland

Grand Bank

southern

Gulf of St. Lawrence

70° 68° 66° 64° 62° 60° 58° 56° 54° 52° 50° 48°40°

41°

42°

43°

44°

45°

46°

47°

48°

49°

50°

51°

70° 68° 66° 64° 62° 60° 58° 56° 54° 52° 50° 48°40°

41°

42°

43°

44°

45°

46°

47°

48°

49°

50°

51°

Georges Bank

USA Bay of Fundy

St. Margarets BayHalifax

CansoCape Breton Island

Hell Hole

New Brunswick

Nova Scotia

P.E.I.

Newfoundland

Grand Bank

southern

Gulf of St. Lawrence

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2005

2007

2006

Figure 2. The location of catches of bluefin tuna in the Gulf of St. Lawrence from log record data for

2005 to 2007.

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68° 66° 64° 62° 60° 58° 56° 54° 52° 50° 48° 46°

40°

42°

44°

46°

48°

0

1

5

10

25+

2005

68° 66° 64° 62° 60° 58° 56° 54° 52° 50° 48° 46°

40°

42°

44°

46°

48°

0

1

5

10

25+

2006

Figure 3. Canadian bluefin catch (numbers) by the tended line, rod and reel and electric harpoon fisheries off Nova Scotia, from log record data aggregated by 10 minute rectangles for 2005 (top), 2006 (middle) and 2007 (bottom).

68° 66° 64° 62° 60° 58° 56° 54° 52° 50° 48° 46°

40°

42°

44°

46°

48°

0

1

5

10

25 +

2007

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Figure 4. Canadian bluefin catch (numbers) by the pelagic longline fishery off Nova Scotia, from log record

data aggregated by 10 minute rectangles for 2005 (top), 2006 (middle) and 2007 (bottom).

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Figure 5. Canadian bluefin catch (numbers) off Newfoundland by tended line and rod and reel, from log

record data aggregated by 10 minute rectangles for 2002-2004 (top), shown in comparison to the 2005-2007 aggregated data (bottom).

-60 -58 -56 -54 -52 -50 -48 -46 -44 -42 -40 -38 -3640

41

42

43

44

45

46

47

48

49

50

51

52

53

54

1

10

50

100

2002-2004

-60 -58 -56 -54 -52 -50 -48 -46 -44 -42 -40 -38 -3640

41

42

43

44

45

46

47

48

49

50

51

52

53

54

1

10

50

100

2005-2007

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Figure 6. Canadian landings of bluefin tuna compared with quota, 1989 – 2007.

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0

20

40

60

80

100

120

140

160

PEINFL

GulfNB PQ

GulfNS

SWNSSMB

Offshore

PelLL

Fleet Sector

Met

ric T

ons

CaughtFleet Quota

Fig. 7. The catch of the Canadian fleet sectors relative to quota for 2007.

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Active Vessels - Gulf of St. Lawrence

0

50

100

150

200

250

300

350

400

1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

Year

# A

ctiv

e

Rod and ReelTended LineUnassigned

Active Vessels - SouthWest Nova Scotia

0

50

100

150

200

250

300

1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

Year

# Ac

tive

Rod and ReelTended LineHarpoonUnassigned

Figure 8. Trends in number of vessels in the Canadian bluefin tuna fisheries by area and gear type. The pelagic longline

component is not shown in these plots.

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SWNS Tended Line FisheryAugust & September n=3349

1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008

Rou

nd w

eigh

t (kg

)

0

100

200

300

400

500

600

Gulf of St. Lawrence Rod & Reel FisheryAugust & September n=4321

1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008

Rou

nd w

eigh

t (kg

)

0

100

200

300

400

500

600

700

Figure 9. Trends in median weight (upper and lower edges of the box represent 75 and 25th percentiles of the data in each year, and the upper and lower “whiskers” signify the 95 and 5th percentiles, respectively) shown by gear and area for bluefin tuna captured in Canadian fisheries. SWNS = southwest Nova Scotia.

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Leng

th F

requ

ency

(%)

0

10

20

3040

1999

0

10

20

3040

2000

0

10

20

3040

2001

0

10

20

30

40

2002

0

10

20

30

40

2003

0

10

20

30

40

2004

X Data

0

10

20

30

40

2005

0

10

20

30

40

2006

Curved Fork Length (cms)

50 100 150 200 250 300 350 4000

10

20

30

40

2007

Age 10 12 14 16 18

Figure 10. Length-frequency distribution of the landings of bluefin tuna in the southern Gulf of St. Lawrence. For reference, the lengths at age predicted by the Turner and Restrepo (1994) growth model are shown for selected ages.

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Figure 11. Condition of Atlantic bluefin tuna in the southern Gulf of St. Lawrence, standardized for year, month

and length class, 1974 – 2007. Mean +/- 1 S.E is plotted.

1970 1975 1980 1985 1990 1995 2000 20051.5

1.6

1.7

1.8

1.9

2.0

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Bluefin Catch per Trip

0 5 10 15 20

Pti

0.0

0.2

0.4

0.6

0.8

1.0

Gulf (n = 81,040)SWNS (n = 5,347)

Figure 12. Frequency distributions (percent) of bluefin tuna catch per trip used in the development of

CPUE indices for the Southwest Nova Scotia (Hell Hole and Bay of Fundy, 1988-2007) and Gulf of St. Lawrence (1981-2007) fisheries.

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Figure 13. Diagnostic plots for the delta lognormal-binomial model formulation. The top panels show the frequency distribution of the log transformed nominal CPUE for positive trips for the Gulf of St Lawrence (upper) and Southwest Nova Scotia (lower) series. The bottom plots show the normalized cumulative residuals (or qq-plots) of the fit for the positive trips in the delta lognormal model component; the expected trend is a straight line.

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Bluefin Tuna Gulf St Lawrence

0

1

2

3

4

5

6

1980 1985 1990 1995 2000 2005 2010

Scal

ed C

PUE

(fish

per

100

hou

rs)

Standardized

Nominal

Figure 14. Standardized CPUE indices (Table 4) for the Gulf of St. Lawrence fishery from the delta

lognormal-binomial model formulation. Nominal catch rates are also shown. Series are scaled to their mean. Thin lines are the 95% CI.

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Nova Scotia Bluefin Tuna Standardized Cpue

0

1

2

3

4

5

6

7

8

1985 1990 1995 2000 2005 2010

Scal

ed C

PUE

(fis

h pe

r 10

0 ho

urs)

SW-NS

Nominal

Figure 15. Comparison of standardized CPUE indices (Table 5) for the Southwest Nova Scotia fishery using the

delta lognormal-binomial model formulation. Nominal catch rates are also shown. Series are scaled to their mean. Thin lines are the 95% CI.