INDICES OF STOCK STATUS OBTAINED FROM THE CANADIAN BLUEFIN TUNA FISHERY

Transcription

1 SCRS/2008/083 Collect. Vol. Sci. Pap. ICCAT, 64(2): (2009) INDICES OF STOCK STATUS OBTAINED FROM THE CANADIAN BLUEFIN TUNA FISHERY J.D. Neilson 1, S. Smith 1, M. Ortiz 2, and B. Lester 3 SUMMARY Updated standardized relative abundance indices are presented for Canadian bluefin tuna fisheries in the Gulf of St. Lawrence ( ) and off Southwest Nova Scotia ( ) 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. RÉSUMÉ Ce document présente les indices standardisés de l abondance relative des pêcheries canadiennes de thon rouge dans le Golfe du St Laurent ( ) et au sud-ouest de la Nouvelle Ecosse ( ), sur la base des enregistrements commerciaux. Les méthodes utilisées étaient les mêmes que celles de l évaluation du stock de thon rouge de Une régression pas à pas a été utilisée pour déterminer les spécifications du modèle delta lognormal-binomial les plus appropriées pour standardiser les deux séries de CPUE. Les CPUE du Golfe du St Laurent se sont légèrement accrues de 1997 à 2003, puis ont rapidement augmenté en 2004 et sont restées élevées depuis lors. Les taux de capture en 2007 sont les plus élevés de la série temporelle ; ils sont près de trois fois plus élevés que la moyenne de la série. La série du sud-ouest de la Nouvelle Ecosse présentait une tendance assez stable du milieu jusqu à la fin des années Alors que l an 2000 présentait la valeur la plus faible enregistrée, les taux de capture ont, depuis, suivi une tendance légèrement ascendante. Les taux de capture de 2007 sont proches (0,98) de la moyenne de la série. La distribution spatiale des pêcheries canadiennes n a pas beaucoup changé, mais on a signalé de manière anecdotique que des thons sont apparus dans des zones où ils n avaient pas été observés depuis de nombreuses années (par exemple, la Baie des Chaleurs à l ouest du Golfe du St Laurent). La composition par taille de la capture dans le sud du Golfe du St Laurent, au cours des 5-6 dernières années, a généralement suivi une tendance à la baisse qui s est récemment stabilisée, et qui est désormais en hausse. La condition (K de Fulton) des poissons individuels dans le sud du Golfe du St Laurent suit une tendance à la baisse et dégage maintenant les plus faibles valeurs de la série. RESUMEN 1 Fisheries & Oceans Canada, Biological Station, 531 Brandy Cove Road, St. Andrews, NB E5B 2L9 Canada. 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, U.S.A. 3 Fisheries & Oceans Canada. 380

2 Se presentan índices de abundancia relativa estandarizados y actualizados para las pesquerías canadienses de atún rojo en el Golfo de San Lorenzo ( ) y en las aguas del Suroeste de Nueva Escocia ( ), obtenidos a partir de los datos de los registros de los cuadernos de pesca comerciales. Los métodos utilizados son los mismos que los de la evaluación de stock de atún rojo de Se utilizó una regresión gradual para determinar las especificaciones más apropiadas del modelo binomial delta lognormal para estandarizar ambas series de CPUE. Las CPUE en el Golfo de San Lorenzo se incrementaron ligeramente desde 1997 hasta 2007, aumentaron rápidamente en 2004 y han mantenido valores elevados desde entonces. Las tasas de captura de 2007 son las más elevadas de la serie temporal, casi triplicando el valor promedio de la serie. Las series del Suroeste de Nueva Escocia han mantenido una tendencia bastante estable desde mediados a finales de los noventa. Aunque en 2000 se observó el valor más bajo registrado, las tasas de captura han seguido una tendencia ligeramente creciente desde entonces. Las tasas de captura de 2007 son similares (0,98) a la media de la serie. La distribución espacial de las pesquerías canadienses no han cambiado significativamente, pero hubo informes anecdóticos de presencia de túnidos en zonas en las que no se habían observado en muchos años (por ejemplo, Baie des Chaleurs en la parte occidental del Golfo de San Lorenzo). En los últimos cinco o seis años, la composición por tallas de la captura en la parte meridional del Golfo de San Lorenzo ha seguido una tendencia generalmente decreciente que se ha estabilizado hace poco y que se está incrementando actualmente. La condición (K de Fulton) de ejemplares individuales en el Golfo de San Lorenzo meridional ha estado siguiendo una tendencia decreciente y se sitúa actualmente en el valor más bajo de la serie. KEYWORDS Tuna fisheries catch rates, size composition 1. 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. 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 (Figure 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 (Figure 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 (Figure 3) from 2005 to 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 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 (Figure 4), moved further offshore to target tropical tunas and to avoid 381

3 excessive catches of swordfish, which were abundant in 2006 and The distribution of the tended line and rod and reel fishery off southern Newfoundland has not changed appreciably in recent years (Figure 5) Annual landings and Canadian quotas are shown in Figure 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 Figure 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. Trends in fishing capacity The number of license holders eligible to land bluefin tuna was 776 from , 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 Figure 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. 4. 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 0% coverage of properly completed log records and individual fish sizes. In actuality, 94% of individual bluefin landed in 2007 had associated size information. 5. 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 (Figure 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 The 2005 fishery, as seen in Figure 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 Figure. The length composition information reflects the trends in median weight described above, in general. In 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 to

4 6. Condition of the catch We calculated the trend in condition (Fulton s K, ((W/L 3 )*0,000)), after standardizing for effects of length class, month and year (Figure 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. 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 ( ), and Southwest Nova Scotia tended line/harpoon/rod and reel (=Hell Hole plus Bay of Fundy, ). Based on the von Bertalanffy 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 Gulf of St. Lawrence Series The Gulf of St. Lawrence standardized index was based on catch and effort data for vessels with + trips per year and included observations for 27 years ( ), three months (August, September, October), two fleets (Prince Edward Island and Gulf Nova Scotia) and two gear types (tended line, rod and reel) (n= trips). The + 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 (Figure 12; Stone et al. 2001) Southwest Nova Scotia Series Catch and effort data aggregated by trip from the Hell Hole ( ) and Bay of Fundy ( ) 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 (Figure 7). The data set used for CPUE standardization included observations for 20 years ( ), 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). 7.2 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 χ 2 (Chisquare) distribution. This statistic was used to test for the significance of an additional factor in the model. The 383

5 number of additional parameters associated with the added factor minus one corresponds to the number of degrees of freedom in the χ 2 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 χ 2 test significance, and c) the Type III test significance within the final specified model. 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 Figure 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 deltabinomial method with random effects to produce a single index included the following variables (see Figure 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 7.3 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 (Figure 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 (Figure 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. The standardized series for both the Gulf of St. Lawrence and Southwest Nova Scotia follow the nominal series closely (Tables 4, 5; Figures 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. 384

6 8. Commentary from fishing industry Industry consultations occurred in Dartmouth, Nova Scotia (May 27 th, 2008) and Charlottetown, Prince Edward Island (June 3 rd, 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 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 These anecdotal reports are supported by reports from fishery observers. A summary of the views obtained during the two consultations is given in Table

7 9. 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 postspawning 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 (>%) 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.. Literature cited Anon Report of the 2006 ICCAT SCRS bluefin tuna stock assessment session. Collect. Vol. Sci. Pap. ICCAT, 60(3): Calcutt, M., Paul, S., Neilson, J., and McMaster, A., National Report of Canada, Int. Comm. Conserv. Atl. Tunas ANN-006/2005. Dutil, J.D. and Lambert, Y., Natural mortality from poor condition in Atlantic cod (Gadus morhua). Canadian Journal of Fisheries and Aquatic Sciences. 57(4): Golet, W.J., Cooper, A., Campbell, R. and Lutcavage, M., Decline in condition factor of Atlantic bluefin tuna (Thunnus thynnus) in the Gulf of Maine. Fish. Bull. 5: Kjesbu, O.S., Whitthames, P.R., Solemdal, P. and Greer Walker, M., 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, Littell, R.C., Milliken, G.A., Stroup, W.W. and Wolfinger, R.D., SAS System for Mixed Models, Cary NC: SAS Institute Inc., pp. Lo, N.C., Jacobson, L.D. and Squire, J.L., Indices of relative abundance from fish spotter data based on delta-lognormal models. Can. J. Fish. Aquat. Sci. 49; Mccullagh, P. and Nelder, J.A Generalized Linear Models 2 nd edition. Chapman & Hall. Neilson, J.D., Paul, S.D. and Ortiz, M., Indices of stock status obtained from the Canadian bluefin tuna fishery. Collect. Vol. Sci. Pap. ICCAT, 60(3): Porter, J.M., Ortiz, M. and Paul, S.D., Updated standardized CPUE indices for Canadian bluefin tuna fisheries based on commercial catch rates. Collect. Vol. Sci. Pap. ICCAT, 55(3): SAS Institute Inc. 1997, SAS/STAT Software: Changes and Enhancements through Release Cary, NC:Sas Institute Inc., pp. Stone, H.H., Ortiz, M. and Porter, J.M., Updated standardized CPUE indices for Canadian bluefin tuna fisheries. Collect. Vol. Sci. Pap. ICCAT, 52 (3):

8 Turner, S.C., and Restrepo, V.R A review of the growth rate of west Atlantic bluefin tuna, Thunnus thynnus, estimated from marked and recaptured fish. Collect. Vol. Sci. Pap. ICCAT, 42 (1): (1994). Table 1. Summary of step-wise regression analyses used for determining the most appropriate delta lognormalbinomial 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 values Degrees of freedom Residual deviance Change in deviance % of total deviance p Year % < Year Month % Year Month Gear % 0.8 Year Month Gear Fleet % < Year Month Gear Fleet Month*Fleet % Year Month Gear Fleet Month*Gearc % Year Month Gear Fleet Year*Gearc % Year Month Gear Fleet Gearc*Fleet % 0.0 Year Month Gear Fleet Year*Fleet % Year Month Gear Fleet Year*Month % Model factors proportion positives Degrees of freedom Residual deviance Change in deviance % of total deviance p Year % < Year Month % < Year Month Fleet % < Year Month Fleet Gearc % < Year Month Fleet Gearc Month*Fleet % < Year Month Fleet Gearc Month*Gearc % < Year Month Fleet Gearc Fleet*Gearc % < Year Month Fleet Gearc Year*Fleet % < Year Month Fleet Gearc Year*Gearc % < Year Month Fleet Gearc Year*Month % <

9 Table 2. Summary of step-wise regression analyses used for determining the most appropriate delta lognormalbinomial 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 Year % < Year Month % Year Month Area % Year Month Area Gear % Year Month Area Gear Fleet % Year Month Area Gear Fleet Area*Fleet % Year Month Area Gear Fleet Month*Area % Year Month Area Gear Fleet Month*Fleet % Year Month Area Gear Fleet Month*Gear % < Year Month Area Gear Fleet Year*Area % < Year Month Area Gear Fleet Year*Gear % < Year Month Area Gear Fleet Year*Month % < Year Month Area Gear Fleet Year*Fleet % < Model factors proportion positives d.f. Residual deviance Change in deviance % of total deviance p Year % < Year Month % < Year Month Area % < Year Month Area Gear % < Year Month Area Gear Fleet % < Year Month Area Gear Area*Fleet % Year Month Area Gear Gear*Fleet % < Year Month Area Gear Year*Area % < Year Month Area Gear Year*Month % < Year Month Area Gear Year*Gear % < Year Month Area Gear Year*Fleet % <

10 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 Likelihood Ratio Test Proportion Positives Year Fleet Month Gear Year Fleet Month Gear Year*Month *** Year Fleet Month Gear Year*Month Year*Gear Year Fleet Month Gear Year*Month Year*Gear Year*Fleet N/A Positive Catch Year Fleet Gear Year Fleet Month Year*Fleet *** Year Fleet Month Year*Fleet Year*Month Southwest Nova Scotia -2 REM Log likelihood Akaike's Information Criterion Schwartz's Bayesian Criterion Likelihood Ratio Test Proportion Positives Year Month Area Fleet Year Month Area Fleet Year*Area Year Month Area Fleet Year*Area Year*Month *** Year Month Area Fleet Year*Area Year*Month Year*Fleet Positive Catch Year Month Area Gear Fleet Year Month Area Gear Fleet Year*Month E-24 Year Month Area Gear Fleet Year*Month Year*Fleet *** Year Month Area Gear Fleet Year*Month Year*Fleet Year*Gear

11 Table 4. Nominal and standardized (delta lognormal-binomial mixed model) CPUE series (tuna/0 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 + trips annually from August through October, (Nominal CPUE= number of tuna per 0 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

12 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, The index is scaled to the mean of the time series. Year N Obs Hours fished No fish Nominal Index SE CV

13 Table 6. Summary of views obtained during consultations with the bluefin fishing industry prior to the 2008 stock assessment. Positive 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. Negative Indicators 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. 392

14 southern Newfoundland 47 Gulf of St. Lawrence 46 New Brunswick P.E.I. 45 Nova Scotia Cape Breton Island Canso Grand Bank USA Halifax St. Margarets Bay Bay of Fundy 42 Hell Hole Georges Bank 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). 393

15 Figure 2. The location of catches of bluefin tuna in the Gulf of St. Lawrence from log record data for 2005 to

16 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 minute rectangles for 2005 (top), 2006 (middle) and 2007 (bottom). 395

17 Figure 4. Canadian bluefin catch (numbers) by the pelagic longline fishery off Nova Scotia, from log record data aggregated by minute rectangles for 2005 (top), 2006 (middle) and 2007 (bottom). 396

18 Figure 5. Canadian bluefin catch (numbers) off Newfoundland by tended line and rod and reel, from log record data aggregated by minute rectangles for (top), shown in comparison to the aggregated data (bottom). 397

19 Figure 6. Canadian landings of bluefin tuna compared with quota, Metric Tons Caught Fleet Quota PEI NFL GulfNB PQ GulfNS SWNS SMB Offshore PelLL Fleet Sector Figure 7. The catch of the Canadian fleet sectors relative to quota for

20 Active Vessels - Gulf of St. Lawrence Rod and Reel Tended Line Unassigned # Active Year Active Vessels - SouthWest Nova Scotia Rod and Reel Tended Line Harpoon Unassigned 200 # Active Year 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. 399

21 600 SWNS Tended Line Fishery August & September n= Round weight (kg) Gulf of St. Lawrence Rod & Reel Fishery August & September n= Round weight (kg) Figure 9. Trends in median weight (upper and lower edges of the box represent 75 and 25 th percentiles of the data in each year, and the upper and lower whiskers signify the 95 and 5 th percentiles, respectively) shown by gear and area for bluefin tuna captured in Canadian fisheries. SWNS = southwest Nova Scotia. 400

22 Age Length Frequency (%) X Data Curved Fork Length (cms) Figure. 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. 401

23 Figure 11. Condition of Atlantic bluefin tuna in the southern Gulf of St. Lawrence, standardized for year, month and length class, Mean +/- 1 S.E is plotted Gulf (n = 81,040) SWNS (n = 5,347) 0.6 P ti Bluefin Catch per Trip 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, ) and Gulf of St. Lawrence ( ) fisheries. 402

24 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 qqplots) of the fit for the positive trips in the delta lognormal model component; the expected trend is a straight line. 403

25 Bluefin Tuna Gulf St Lawrence Scaled CPUE (fish per 0 hours) Standardized Nom inal Figure 14. Standardized CPUE indices (Table 4) for the Gulf of St. Lawrence fishery from the delta lognormalbinomial model formulation. Nominal catch rates are also shown. Series are scaled to their mean. Thin lines are the 95% CI. Nova Scotia Bluefin Tuna Standardized Cpue 8 Scaled CPUE (fish per 0 hours) 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. 404