UPDATED NOMINAL CPUE INDICES AND A PRELIMINARY COMBINED INDEX OF ABUNDANCE FOR THE CANADIAN BLUEFIN TUNA FISHERIES:

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1 SCRS/2015/047 Collect. Vol. Sci. Pap. ICCAT, 72(6): (2016) UPDATED NOMINAL CPUE INDICES AND A PRELIMINARY COMBINED INDEX OF ABUNDANCE FOR THE CANADIAN BLUEFIN TUNA FISHERIES: I. Andrushchenko 1 and A.R. Hanke 1 SUMMARY The updated nominal indices of abundance of Atlantic Bluefin tuna from the Canadian rod and reel, tended line and harpoon fisheries show a decrease from 2013 levels. These trends seem linked to a redistribution of fishing effort outside of the geographical scope of the index, as well as a shift in the size composition of the fisheries. A preliminary index of abundance for Bluefin tuna fisheries in Canadian waters is presented, combining the existing two indices with data which has been historically excluded. RÉSUMÉ Les indices nominaux mis à jour de l'abondance du thon rouge de l'atlantique provenant des pêcheries canadiennes de canne et moulinet, de ligne surveillée et au harpon présentent une diminution par rapport au niveau de Ces tendances semblent liées à une redistribution de l'effort de pêche en dehors de la portée géographique de l'indice ainsi qu'à un changement de la composition des tailles des pêcheries. Un indice préliminaire de l'abondance des pêcheries de thon rouge dans les eaux canadiennes est présenté en combinant les deux indices existants avec des données qui avaient été historiquement exclues. RESUMEN Los índices nominales actualizados de abundancia de atún rojo del Atlántico de las pesquerías canadienses de caña y carrete, barrilete y arpón muestran un descenso respecto a los niveles de Estas tendencias parecen estar vinculadas con una redistribución del esfuerzo de pesca fuera de la zona geográfica del índice, así como con un cambio en la composición por tallas de las pesquerías. Se presenta un índice preliminar de abundancia en las pesquerías de atún rojo en aguas canadienses, combinando los dos índices existentes con los datos que se han excluido históricamente. KEYWORDS Catch Rates, Size Composition, Bluefin tuna, Rod and Reel 1. Description of the data source 1.1 Description of the fishery and target species The Canadian commercial Bluefin tuna fisheries target bluefin tuna migrating into Canadian waters between the months of July and November. The 2014 spatial distribution of the two main fisheries occurring off the coast of southwestern Nova Scotia (SWNS) and in the southern Gulf of St. Lawrence (sgsl) has remained consistent with that of previous years (Figure 1). Outside of the these two fisheries, catches occur along the east coast of Nova Scotia, with the majority being conducted around St. Margaret s Bay/Halifax and Canso areas (Figure 1). The SWNS fishery generally takes place between the months of August and October, though in recent years the season has been skewed towards October (Figure 2). This fishery continues to be dominated by rod and reel catches, with smaller contributions by tended line and harpoon (Figure 3). The Scotia-Fundy (SF) home fleet continues to account for 80% of the catches in SWNS, due to decreased activity by ex-sector fleets (Figure 4). 1 Fisheries & Oceans Canada, Biological Station, 531 Brandy Cove Road, St. Andrews, NB E5B 2L9 Canada. address of lead author: alex.hanke@dfo-mpo.gc.ca. 1412

2 Similarly, the sgsl fishery season spans the months of August October, with high activity in the later months (Figure 2). The catches are made almost exclusively by rod and reel gear (Figure 3), with the home fleets (GNB, GNS, PQ and PEI) responsible for ~95% of the trips (Figure 4). Fishing activity in NAFO areas 4VW has been historically excluded from both indices (Figure 1). In the 1990s the fishing in 4VW season spanned the months of August through October (Figure 2). More recently, the competitive management structure of the fishery in 4Wd combined with the timing of tuna coming out of the Gulf of St. Lawrence have compressed and delayed the season to the second half of October and into November. 4VW is fished almost entirely by rod and reel gear, though some harpoon catches appear in recent years (Figure 3). The 4VW area is fished by a variety of fleets, with the GNS fleet becoming predominant in the last two years (Figure 4). 1.2 Size, age range and condition of the fish that the index applies to Fish caught in the Southwest Nova Scotia fishery have shown a general increase in round weight throughout the 2000s, up to a series maximum mean weight of 251 kgs in 2013 (25 th and 75 th percentiles at 179 kgs and 319 kgs respectively) (Figure 5). In 2014, the mean weight of the catch decreased to 200 kgs (25 th and 75 th percentiles at 150 kgs and 247 kgs respectively), but remains above the series mean of 172 kgs. The round weight of catch in the southern Gulf of St. Lawrence fishery has remained below the series mean of 350 kgs since 2010 (Figure 5). The mean catch weight for 2014 is the lowest for the series (281 kgs, with 25 th and 75 th percentiles at 228 kgs and 336 kgs respectively), and has been attributed to a particularly strong year class moving through the fishery (Figure 6). Fishermen indicate that a shift in the distribution of larger fish may also contribute to the uncharacteristically low mean weight (see Section 1.5). Recent weight trends in both fisheries are attributed to the redistribution of Bluefin stock components within the Canadian EEZ. This work is currently being explored on a broader geographical scale, and is complemented by fish movements in 4VW and further east in 3LNOP (Figure 7). 1.3 Changes in the fishery that might affect catch rates The mandatory submission of logbooks was instituted in 1996 and the move from a competitive fishery to an Individual Transferrable Quota (ITQ) system began in 2004 for the southwest Nova Scotia fleet. The main fleet fishing in the southern Gulf of St. Lawrence (PEI) adopted an ITQ-like system in Fishing within 4W is subject to management structure of SWNS, except in 4Wd where the fishery continues to operate in a competitive manner. Historical catches in 4V are subject to restrictions of the sgsl fleet. According to industry feedback, market demand for a given size class of tuna has had some effect on the SWNS fishery s harvest decisions in Similarly, fishermen from the sgsl fleets have indicated that large bluefin tuna have moved north in the Gulf of St. Lawrence, while the smaller individuals remain in southern waters. 2. Methods 2.1 Data Exclusions and Rationale Both the SWNS and the sgsl datasets were filtered in order to restrict the data to views established in the past. The SWNS fishery index was limited to catches made by tended line, rod and reel and harpoon, excluding catches made by the trapnet fleet in St. Margaret s Bay. Geographically, the data were limited to NAFO areas 4X, 5Y and 5Z (Figure 1, Figure 7), while excluding 4Xm and 4Xu (St. Margaret s Bay / Halifax). Finally, the season for the SWNS index was limited to the months of August, September and October. Similarly, the sgsl index was limited to rod and reel / tended line, and the months of August, September and October. Geographically, sgsl data was bounded by a box of 68 W to 60 W longitude, and 46 N to 50 N latitude (Figure 1, Figure 7). 1413

3 The combined index was restricted to rod and reel, tended line and harpoon gears, excluding catches made by the trapnet fleet. The index included the months of July through November, and was limited to years With additional work, the combined index could be expanded to Catches landed by the Newfoundland fleet (ex-sector) were removed from all datasets because these vessels behave in a manner inconsistent with the other fleets. 2.2 Management Regulations There have been two major changes in the management of the Canadian Bluefin tuna fishery: 1) the introduction of mandatory log submissions in the mid-1990s and 2) the switch to an Individual Transferable Quota (ITQ) fishery in the early 2000s (SWNS, some 4W) and 2010s (sgsl). Starting in 1996, mandatory log submissions provided detailed information on all trips targeting Bluefin tuna in Canadian waters, including trips with no catch; prior to 1996, this information was submitted on a voluntary basis. 2.3 Dataset used in the Analysis A summary of data for the SWNS, sgsl and combined datasets are provided in Table The effort and catch variables In both the SWNS and sgsl nominal indices, hours fished have been used as the measure of effort (Paul et al. 2010), while the catch variable was a count of Bluefin tuna caught, aggregated to trip. For the joint index, the trip-level data by fishing area within the Canadian EEZ produced different catch effort relationships (Figure 8). These differences are largely a function of the fishing behaviors in each area and restrictions imposed on the fishing by management measures. The sgsl (4RST) fishery was limited to a single fish per trip and trips were less than a day long. This is different from SWNS (4X5Z) where trips are multi-day and more fish can be landed per trip. Aggregating catch and effort data from nafo areas 4RST (Gulf of St. Lawrence) by calendar day, gear and port seems to make the catch effort relationship more similar across areas ( Figure 9). Additional measures are being investigated. 2.4 Model Standardization and Diagnostics A negative binomial model, which included year, NAFO area and month, was fit to the combined Bluefin tuna count data, with log (hours fished) as an offset. This preliminary model has patterns in the residuals (Figure 10) and more complicated models addressing this have failed to converge. Additional work is required developing a final model before any conclusions can be drawn. 3. Results 3.1 Nominal Nominal indices of abundance for the SWNS fishery showed a decline in 2014 (Figure 11). The high mean catch weight, thought to have contributed to the index decrease in 2013, has returned to normal levels in 2014, indicating that the redistribution of effort into 4W may have a greater impact on SWNS CPUE than previously thought (Table 3). The sgsl nominal CPUE index has also decreased, but remains far above the levels seen prior to the 2010 season. A combination of a strong year class and movement of larger individuals to feeding grounds in the northern Gulf of St. Lawrence (Baie des Chaleurs) is thought to contribute to this trend. 3.2 Standardized combined index The combined index is a preliminary attempt at generating a single index of abundance for the Canadian Bluefin tuna fisheries. Although this index is subject to the caveats identified within each of the individual indices (management structure, targeting, season fragmentation, etc.), it does successfully address changes in season expansion and effort redistribution into 4W. The area specific indices are shown in Figure 12 and are based on fixing effort at 12 h and month as September. 1414

4 The standardized index requires additional work before any concrete conclusions can be drawn. 4. Research Recommendations Consideration should be given to estimating the effect of changes in management structure on all three indices, as well as accounting for possible targeting of other tunas in the SWNS fishery (Hanke et al. 2012). It is also important to revisit catch data prior to 1996 to determine the amount the zero-catch trips that should be present in the data. A redistribution of both fishing effort and population components (Hanke et al. 2014) warrants a reanalysis of both the SWNS and sgsl fisheries without the temporal and geographical restrictions historically imposed on these indices. The combined Canadian Bluefin index has potential for addressing the limitations associated with the individual Canadian fisheries indices. Further work into the standardization process is currently underway, and may lead to producing an index on a larger geographical scale. References Hanke, A.R., I. Andrushchenko, and C. Whelan Indices of stock status from the Canadian Bluefin Tuna Fishery. SCRS/2012/118. Hanke, A.R., I. Andrushchenko, and C. Whelan Indices of stock status from the Canadian Bluefin Tuna Fishery: 1981 to SCRS/2014/039. Paul, S. D., A.R. Hanke, A.S.M. Vanderlaan, D. Busawon, and J.D. Neilson Indices of Stock Status from the 2009 Canadian Bluefin Tuna Fishery. SCRS/2010/070. Zeileis, A and T. Hothorn (2002). Diagnostic Checking in Regression Relationships. R News 2(3), URL

5 Table 1. Dataset description for the Southwest Nova Scotia bluefin tuna fishery. month hma gear area YEAR AUG SEP OCT GNB GNS PEI PQ SF HP RR TL 4X 5Y 5Z

6 Table 2. Dataset description for the southern Gulf of St. Lawrence bluefin tuna fishery. month hma gear YEAR AUG SEP OCT GNB GNS PEI PQ SF RR TL

7 Table 3. Dataset description for the combined index of abundance for the Canadian bluefin tuna fishery. month hma gear area management YEAR JUL AUG SEP OCT NOV GNB GNS PEI PQ SF HP RR TL 3LNOP 4RST 4VW 4X5YZ COMP ITQ

8 Figure 1. Historic distribution of trips in the Southwest Nova Scotia(SWNS) and Southern Gulf of St. Lawrence (sgsl) bluefin fisheries between 1981 and 2013, in multi-year intervals; bottom panel is limited to the 2014 season. Blue polygons show historic NAFO area limitations for each fishery. 1419

9 Figure 2. Season progression using proportion of trips by month within a given year in the Southwest Nova Scotia (top) and Gulf St. Lawrence (middle) and 4VW (bottom) Bluefin tuna catch data. The month restriction has been relaxed and the solid line indicates switch from competitive to an ITQ-like structure in each fishery. Dashed line indicates when some vessels switched to ITQ. 1420

10 Figure 3. Relative frequency of records gears (tended line, rod and reel, harpoon) within year for the Southwest Nova Scotia (top) and Gulf St. Lawrence (middle) and 4VW (bottom) bluefin tuna fisheries. Historic restrictions apply. 1421

11 Figure 4. Relative frequency of records by year and home management areas (fleets) within year for Southwest Nova Scotia (top) and Gulf St. Lawrence (middle) and 4VW (bottom). Historic restrictions apply. 1422

12 Figure 5. Round weight (kg) of recent catches made in the Southwest Nova Scotia (top) and Gulf of St. Lawrence (bottom) bluefin fisheries. Red line indicates series mean. 1423

13 Figure 6. Catch composition for the sgsl fishery since Vertical line marks series mean ( ) of 350 kgs. 1424

14 Figure 7. Map delimiting major NAFO areas within the Canadian EEZ. 1425

15 Figure 8. Relationship between effort (hours fished) and catch (number of Bluefin tuna) for each unique fishing area where effort and catch for 4RST is aggregated to the trip level. Red dots represent the mean number of hours required to catch each discrete number of fish (0 to 30). Figure 9. Relationship between effort (hours fished) and catch (number of Bluefin tuna) for each unique fishing area where effort and catch for 4RST is aggregated to calendar day by gear and port. Red dots represent the mean number of hours required to catch each discrete number of fish (0 to 30). 1426

16 Figure 10. Plots of standardized residuals from the combined index model. 1427

17 Figure 11. Nominal CPUE indices for SWNS and sgsl fisheries. Figure 12. Preliminary standardized indices and 95% CIs for Canadian fishing areas. The points are the nominal values. 1428