Discarding within the small scale trammel net fishery of Hastings. Daniel Davies

Transcription

1 Discarding within the small scale trammel net fishery of Hastings. Daniel Davies

2 Indirect data collection Self reporting form Three vessels 30 surveyed fishing efforts Four months Species landed in Kg Species discarded in Kg Discard driver Fishing metier Figure 1. Indirect observation, self reporting form.

3 Direct data collection Five direct at sea observations Six months Length Weight Species Number of individuals GPS coordinates Fishing metier Figure 2. The equipment used to record the length and weight data of each discarded specimen. Figure 3. Image of fishing journal used to record all data.

4 Indirectly observed fishing efforts 30 fishing efforts over 99 days V1 = 15 fishing efforts V2 = 9 fishing efforts V3 = 6 fishing efforts Selected 6 fishing efforts from each vessel. 18 fishing efforts over 38 days 60% of recorded fishing efforts over 38% of survey duration Figure 4. Chronological spread of the indirect surveyed fishing efforts conducted by all three fishing vessels. The red lines represent the date boundaries of the effort and date corrected survey.

5 Indirect observation results Figure 5. Mean biomass of total catch per fishing effort for each of the three participating vessels for all surveyed fishing efforts. The total catch is separated into the landed and discarded biomasses. Figure 6. Mean biomass of total catch per fishing effort, for each of the three participating vessels for the date and effort corrected sample. The total catch is separated into the landed and discarded biomasses.

6 Indirect observation results 15 species total catch 5 species discarded catch Discarded population dominated by G. morhua and R. clavata. Figure 7. Biomass of species landed and discarded, for each fishing effort recorded by all three vessels over 38 days.

7 Discarding and its drivers Insufficient quota was reported for all G. morhua, R. clavata and D. labrax discards. Low market value was reported for all P. flesus and S. stellaris discards. Insufficient quota accounted for 93% of all discarded biomass Kg Low market value accounted for 7% of all discarded biomass. 280 Kg Figure 8. Total discarded biomass and the proportional representation of the five discarded species

8 Directly observed fishing efforts Five fishing efforts Six months October to March One fishing effort month -1 excluding December Figure 9. Annotated image of the coastal waters of Hastings depicting the location, date and total length for each of the five surveyed FE. The scale bar represents 1km

9 Direct observation results 18 species across five fishing efforts 14 species discarded G. morhua represents the most discarded biomass. 158 Kg P. platessa represents the most numerous species discarded. n=229 Table 1. biomass and number of individuals for each species recorded during the five directly observed fishing efforts. Biomass in Kg Species Total catch Landed catch Discarded catch Atlantic cod Gadus morhua (n=104) (n=20) (n=84) Plaice Pleuronectes platessa (n=820) (n=591) (n=229) Channel whiting Merlangius merlangus (n=171) (n=171) Dab Limanda limanda (n=77) (n=77) European flounder Platichthys flesus (n=28) (n=28) Thornback ray Raja clavata (n=18) (n=4) (n=14) Lesser spotted dogfish Scyliorhinus canicula (n=5) (n=5) Mackerel Scomber scombrus (n=8) (n=8) Pouting Trisopterus luscus (n=12) (n=12) Smoothhound shark Mustelus asterias (n=1) (n=1) Herring Clupea harengus (n=11) (n=11) Turbot Scophthalmus maximus (n=17) (n=15) (n=2) Common sole Solea solea (n=105) (n=104) (n=1) Ballan wrasse Labrus bergylta (n=1) (n=1) John dory Zeus faber (n=3) (n=3) Brill Scophthalmus rhombus (n=21) (n=21) Tub gurnard Chelidonichthys lucerna (n=1) (n=1) European bass Dicentrarchus labrax (n=1) (n=1) Total (n=1405) (n=761) (n=644) Simpsons index D = 0.63 D = 0.77 DR (%) 69.88% 20.73% 100% 100% 100% 41.42% 100% 100% 100% 100% 100% 6.03% 1.69% 100% 0% 0% 0% 0% 43.00%

10 Mean length and weight The mean length and weight for all discarded individuals Systematic removal of outliers Market forces (Fernandes et al., 2015) Selectivity of 125 mm 2 trammel net (Moth-Poulsen 2003) Figure 10. Mean biomass of discarded individuals. Figure 11. Mean length of discarded individuals.

11 Ecological impact Table 2. the four factors used to calculate ecological impact for each discarded species The mean length and weight was used to calculate the ecological impact of the discarded individuals. Age class, potential fecundity and mass of stomach contents was calculated from the mean length or weight. The trophic level was calculated for the species (Molfese et al., 2014).

12 Ecological impact The four estimated values for age, potential fecundity, trophic level and stomach contents mass allowed each average discarded individual to be ranked by its ecological impacts. G. morhua represented the highest ecological impact for the average discarded individual. P. platessa represented the lowest ecological impact for the average discarded individual. Figure 12. Ranked ecological impact for the nine most abundant species discarded.

13 Discard mortality A high discard mortality replaces previous ecological impacts with a one off input of biomass to detritivore communities (European Union 2014). Many factors influence the discard mortality of a species (Broadhurst et al., 2006). The gadoid and pelagic discarded species have a high discard mortality(suuronen et al., 1995,1996; Benoît et al., 2012). The flatfish and elasmobranch discarded species have a low discard mortality(depestele et al., 2014 Revil et al., 2013). Acute discard mortality within three days Chronic discard mortality occurs over longer time frames(uhlmann and Broadhurst 2015).

14 Discard rate highly variable at all scales of observation from region to individual vessels. A non-exhaustive list of influencing factors include Season Weather Fisher behaviour Quota allocation Conclusions indirect observation Discard rate for Hastings demersal trammel net fishery 65.2% Higher than previous estimates Region VIId (Quirijns and Pastoors., 2014) 13% Small scale fishery 125 mm 2 mesh size (European Parliament 2015a) 10-15% Demersal trammel nets (Siguroardottir et al., 2014) 20-40%

15 Conclusions indirect observation Discarded community dominated by G. morhua and R. clavata Current impact of Article 15 of Common Fisheries Policy The Landings Obligation Low Only M. merluccius and S. solea Future impact of Article 15 of Common Fisheries Policy The Landings Obligation When dominant discarded species are incorporated into Art 15 High G. morhua mean discarded biomass 115 ±SE 20.7 Kg fishing effort -1 R. clavata mean discarded biomass 78.6 ±SE 27.1 kg fishing effort -1 Both species exceeding their monthly total allowable catch quota for November and December in a single fishing effort.

16 Conclusions direct observations Largest impact as a population within discarded community G. morhua n=84 due to large difference in mean size of discarded individual. 2 nd largest impact M. merlangus n=171. P. platessa n=229 most numerous discarded species but with low ecological impact as an individual reducing overall impact. High discard mortality of gadoid species reduces ecological benefits suggested by high fecundity and trophic position. High discard mortality within the higher ecological value species. Low discard mortality within the lower ecological value species. May result in a truncated trophic hierarchy with loss of top down predation control (Heupel et al., 2014).

17 Conclusions High survival of R. clavata combined with high ecological value Discarding of R. clavata aids in restoring top down predation control. Controlling mesopredator populations improving trophic hierarchy Mitigate the higher survival of lower ecological valued mesopredator species Consideration of the exemption of R. clavata from The Landings Obligation Reduces the impact of Article 15 on the Hastings small scale demersal trammel net fishery. Removing potential choke species identified by indirect data.

18 Acknowledgments I would like to thank Dr Corina Ciocan, Paul Joy and Yasmin Ornsby for all their time, support, knowledge and organisation, without which this project would have never got off the ground. I would also like to thank all of the Skippers and crews from the participating vessels. Thank you for your time

19 References Benoît, H., Hurlbut, T., Chassé, J., and Jonsen, I. (2012). Estimating fishery-scale rates of discard mortality using conditional reasoning. Fisheries Research, , pp Broadhurst, M., Suuronen, P., and Hulme, A. (2006). Estimating collateral mortality from towed fishing gear. Fish and Fisheries, 7 (3), pp Depestele, J., Desender, M., Benoît, H., Polet, H., and Vincx, M. (2014). Short-term survival of discarded target fish and non-target invertebrate species in the eurocutter beam trawl fishery of the southern North Sea. Fisheries Research, 154, pp European Parliament. (2015a). Small-scale fisheries and the zero discard target. Brussels: Policy Department B Structural and Cohesion Policies. European Union (2014) Quantifying food subsidies to the benthos due to discards. Institute for Marine Resources and Ecosystem Studies Wageningen UR: Ijmuiden. Fernandes, A., Pérez, N., Prista, N., Santos, J., and Azevedo, M. (2015). Discards composition from Iberian trawl fleets. Marine Policy, 53, pp Moth-Poulsen, T. (2003). Seasonal variations in selectivity of plaice trammel nets. Fisheries Research, 61 (1-3), pp Heupel, M., Knip, D., Simpfendorfer, C., and Dulvy, N. (2014) Sizing up the ecological role of sharks as predators. Marine Ecology Progress Series, 495, pp Molfese, C., Beare, D., and Hall-Spencer, J. (2014). Overfishing and the replacement of demersal finfish by shellfish: an example from the English Channel. Public Library of Science One, 9 (7), e doi: /journal.pone (Accessed on 25th April 2016). Quirijns, F., and Pastoors, M. (ed.) (2014). The discard atlas of North Sea fisheries. Copenhagen: Scheveningen Group. Revill, A., Broadhurst, M., and Millar, R. (2013). Mortality of adult plaice, Pleuronectes platessa and sole, Solea solea discarded from English Channel beam trawlers. Fisheries Research, 147, pp Siguroardottir, S. Stefánsdóttir, E., Condie, H., Margerssona, S., Catchpole, T., Bellido, J., Eliasen, S., Goñi, R., Madsen, N., Palialexish, A., Uhlmanni, S., Vassilopoulou, J., Feekings, J. and Rochet, M.J. (2014) How can discards in European fisheries be mitigated? Strengths, weaknesses, opportunities and threats of potential mitigation methods, Marine Policy, 51. pp Suuronen, P., Lehtonen, E., Tschernijb, V., and Larsson, P. (1995) Skin injury and mortality of Baltic cod escaping from trawl codends equipped with exit windows. Copenhagen: International Council for the Exploration of the Seas Fish Capture Committee. Suuronen, P., Perez-Comas., Lehtonen, E., Tschernij, V. (1996). Size-related mortality of herring (Clupea harengusl.) escaping through a rigid sorting grid and trawl codend meshes. International Council of the Exploration of the Seas Journal of Marine Science, 53 (4), pp Uhlmann, S., and Broadhurst, M. (2015). Mitigating unaccounted fishing mortality from gillnets and traps. Fish and Fisheries, 16 (2), pp