SCRS/2021/015 Collect. Vol. Sci. Pap. ICCAT, 78(1): 62-66 (2021)

DESCRIPTION OF CANADA’S PROPOSED BLUE , / DISCARD ESTIMATION ANALYSES

Kyle M. Gillespie1

SUMMARY

ICCAT Recommendation 19-05 (para. 16) requires that CPCs present to the SCRS a statistical methodology to estimate dead and live discards for blue marlin and white marlin/spearfish. We present three candidate statistical methods to estimate dead and live discards of blue and white . Despite low interaction rates, some or all of the techniques may be appropriate for use in estimating discarding of marlins in Canadian ICCAT fisheries.

RÉSUMÉ

La Recommandation 19-05 de l'ICCAT (paragraphe 16) requiert que les CPC présentent au SCRS une méthodologie statistique pour estimer les rejets morts et vivants des makaires bleus et makaires blancs/ spp. Nous présentons trois méthodes statistiques potentielles permettant d’estimer les rejets morts et vivants de makaires bleus et blancs. Malgré faibles taux d'interaction, certaines ou toutes les techniques pourraient être appropriées pour estimer les rejets de makaires dans les pêcheries canadiennes de l’ICCAT.

RESUMEN

La Recomendación 19-05 de ICCAT (párrafo 16) requiere que las CPC presenten al SCRS una metodología estadística para estimar los descartes vivos y muertos de aguja azul y aguja blanca/Tetrapturus spp. Se presentan tres métodos estadísticos potenciales para estimar los descartes vivos y muertos de aguja azul y aguja blanca. A pesar de las bajas tasas de interacción, algunas o todas las técnicas pueden ser apropiadas para estimar los descartes de marlines en las pesquerías canadienses de ICCAT.

KEYWORDS

Marlin, exploitation, catch statistics

1 Fisheries and Oceans Canada, St. Andrews Biological Station, 125 Marine Science Drive, St. Andrews, NB, Canada, Kyle.Gillespie@dfo- mpo.gc.ca 62

Introduction

As required by ICCAT Recommendation 19-05 (para. 16), Canada will test and may deploy one or more of the following statistical methods to estimate discards of blue marlin and white marlin/roundscale spearfish.

Marlins and spearfish are infrequently encountered in Canadian ICCAT fisheries, which operate near the northern end of their range. In the period 2010 to 2019, Canada’s reported catch for white marlin/spearfish averaged 2.13 mt per year and 0.16 mt/year for blue marlin (Table 1). Observer coverage in the Canadian pelagic fleets is approximately 10% each year and there is 100% dockside observer coverage. Discards, as estimated by onboard observers averages approximately 0.15 mt/year (average 0.12 mt/year DD and 0.17 mt/year DL) for white marlin and 0.07 mt/year for blue marlin (average 0.01 mt/year DD and 0.13 mt/year DL). Low interaction rates for marlins and spearfish (as measured by fisheries observers) may present analysis challenges due to low sample sizes. As a result we will be testing the following discard estimation analyses to determine the most appropriate.

1. Data and methods

1.1 Ratio estimator

A ratio estimation analysis will scale observed discards of marlins and spearfish to the unobserved fishing sets. Multiple ratio estimators will be generated, each accounting for season, fleet type, and eco-region/fishing zone (Figure 1) and catch of target .

Ratio estimation methods are fully described in Appendix V of the 2000 RAP ICCAT Working Group Proceedings (Anonymous, 2000) and Porter et al. (1999). Given that harpooning is selective, there is assumed to be no discarding of marlin/spearfish in this fishery.

The Canadian Atlantic long line fleets fall into two categories: an ITQ fishery that targets and an offshore fishery that primarily targets , unlike the ITQ fishery. Consequently, discard estimates from the ITQ fleet and the Offshore licenses will be calculated separately.

1.2 Random forest model

A random forest model will be tested, training the model on observer data from a recent 10 year period. The following variables will be used to train the model to identify marlin and spearfish trips or sets containing discards: -Season -Eco-zone/fishing zone -Fishing fleet -Sea surface temperature -Set time

1.3 Spatial-temporal GLMM or GAMM

Given sufficient data, a spatial-temporal prediction model will be tested (using e.g. r-inla, vast). The model will use a recent 10 year period of observed fishing sets. We will use variables listed in analysis options 1 and 2 to create the model and then predict discards to the rest of the fishing fleet.

2. Description of data-availability

These statistical methods were developed assuming sufficient marlin and spearfish discard observations in fishing sets. To evaluation whether there are sufficient data for the methods described above, we examining the most recent ten years (2010-2019) of catch and discard data (Tables 2 & 3) from the Maritimes Region pelagic long line fleet. A total of 300 trips were observed out of a total of approximately 2600 trips. Over the ten year span and summed across both observed and observed trip, this gear type interacted with 1,107 white marlin and 130 blue marlin. For white marlin, interactions occurred in 2.85% of sets (486 of 17,038 sets). Interactions occurred in each of the four eco-zones fished by the long line fleets (Figure 1).

63 3. Conclusions

We present three statistical techniques for estimating dead and live discarding of marlins in the Canadian ICCAT fleets. Despite low interaction rates, some or all of the techniques may be appropriate for use in estimating discarding of marlins in Canadian ICCAT fisheries. Testing of these methods is ongoing in 2021.

References

Anonymous. 2000. Meeting of the RAP ICCAT Working Group. Canadian Stock Assessment Secretariat 2000(20): 34pp.

Porter J.M., B.M. Wood, and H.H. Stone. 1999. Preliminary estimation of the tonnage of dead swordfish and bluefin discards from the 1998 Canadian swordfish longline fishery. Collect Vol. Sci. Pap. ICCAT 51(5): 1460-1468.

64 Table 1. Landed catch (mt) of white marlin and blue marlin in Canadian ICCAT fisheries, 2010-2019.

Year WHM (mt) BUM (mt)

2010 1.900 0 2011 0.757 0 2012 2.291 0 2013 2.699 0 2014 4.609 0.493 2015 2.621 0.465 2016 1.155 0.107 2017 2.300 0.281

2018 1.438 0.180

2019 1.495 0.056

Table 2. Number of white marlin landed and discarded in observed and non-observed Maritimes Region pelagic long line trips, 2010-2019.

Observed trips Non-observed trips Year N trips Landed DD DL N trips Landed DD DL 2010 21 0 3 5 209 99 - - 2011 32 1 0 1 218 33 - - 2012 37 0 9 6 228 246 - - 2013 17 1 7 2 217 98 - - 2014 15 9 5 17 253 74 - -

2015 27 5 2 15 254 71 - -

2016 37 3 4 2 242 51 - - 2017 31 4 4 11 258 83 - - 2018 45 0 8 2 222 75 - - 2019 38 0 2 1 215 148 - - Total 300 23 44 62 2316 978 - -

Table 3. Number of blue marlin landed and discarded in observed and non-observed Maritimes Region pelagic long line trips, 2010-2019.

Observed trips Non-observed trips Year N trips Landed DD DL N trips Landed DD DL 2010 21 2 0 3 209 10 - -

2011 32 0 0 0 218 0 - -

2012 37 4 2 12 228 2 - - 2013 17 0 1 2 217 1 - - 2014 15 0 1 3 253 13 - - 2015 27 1 0 1 254 20 - - 2016 37 0 0 0 242 5 - - 2017 31 5 1 2 258 12 - - 2018 45 2 0 3 222 12 - - 2019 38 0 0 0 215 10 - - Total 300 14 5 26 2316 85 - -

65

Figure 1. Set locations (after privacy screening) for Canadian Maritimes Region pelagic longline catch 2010- 2019. Grey dots are locations for sets (observed and not observed) that did not interact with white marlin (n=16,552). Blue dots are locations for sets (observed and not observed) that did interact with white marlin (n=486). The main fishing areas for Canadian pelagic fleets: Emerald basin, Shelf break, Grand Banks and Gulf Stream.

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