Effects of environmental parameters and fishing practices on long-line swordfish catches in the eastern Mediterranean G.Tserpes 1, P.Peristeraki 1, C.Koutsikopoulos 2 HCMR 1, Univ. of Patras 2, Greece EBFMtuna-October 15, 2012 G.Tserpes 1, P.Peristeraki 1, C.Koutsikopoulos 2 (HCMR 1 Effects, Univ. of offishing Patraspractices 2, Greece ) EBFMtuna-October 15, 2012 1 / 19
Study Objectives Evaluate the impact of fishing practices on juvenile swordfish to identify appropriate mitigation measures G.Tserpes 1, P.Peristeraki 1, C.Koutsikopoulos 2 (HCMR 1 Effects, Univ. of offishing Patraspractices 2, Greece ) EBFMtuna-October 15, 2012 2 / 19
Background m Juveniles dominate the Mediterranean swordfish catches (50-70% in terms of numbers, 20-35% in terms of weight) 2 G.Tserpes1, P.Peristeraki1, C.Koutsikopoulos2 (HCMR1Effects, Univ.ofoffishing Patraspractices, Greece ) EBFMtuna-October 15, 2012 3 / 19
Experimental tools m Fishing trials with long-lines equipped with temperature depth recorders (TDR) and hook timers 2 G.Tserpes1, P.Peristeraki1, C.Koutsikopoulos2 (HCMR1Effects, Univ.ofoffishing Patraspractices, Greece ) EBFMtuna-October 15, 2012 4 / 19
Field work m Eastern Mediterranean - Period: June 2010 - August 2011 2 G.Tserpes1, P.Peristeraki1, C.Koutsikopoulos2 (HCMR1Effects, Univ.ofoffishing Patraspractices, Greece ) EBFMtuna-October 15, 2012 5 / 19
Field work m Eastern Mediterranean - Period: June 2010 - August 2011 m 31 Longline sets, 18000 hooks in total 2 G.Tserpes1, P.Peristeraki1, C.Koutsikopoulos2 (HCMR1Effects, Univ.ofoffishing Patraspractices, Greece ) EBFMtuna-October 15, 2012 5 / 19
Fish captures 212 responses from hooktimers G.Tserpes 1, P.Peristeraki 1, C.Koutsikopoulos 2 (HCMR 1 Effects, Univ. of offishing Patraspractices 2, Greece ) EBFMtuna-October 15, 2012 6 / 19
Swordfish captures G.Tserpes 1, P.Peristeraki 1, C.Koutsikopoulos 2 (HCMR 1 Effects, Univ. of offishing Patraspractices 2, Greece ) EBFMtuna-October 15, 2012 7 / 19
Swordfish size distribution G.Tserpes 1, P.Peristeraki 1, C.Koutsikopoulos 2 (HCMR 1 Effects, Univ. of offishing Patraspractices 2, Greece ) EBFMtuna-October 15, 2012 8 / 19
Size variations of swordfish specimens Effect of Depth, Temperature, Time, Moon phase and Month on swordfish Length (LJFL) GAM modelling (stepwise approach) Final Model(gamma error): LJFL = Month + Temperature + s(depth) G.Tserpes 1, P.Peristeraki 1, C.Koutsikopoulos 2 (HCMR 1 Effects, Univ. of offishing Patraspractices 2, Greece ) EBFMtuna-October 15, 2012 9 / 19
Modelling results: Length G.Tserpes 1, P.Peristeraki 1, C.Koutsikopoulos 2 (HCMR 1 Effects, Univ. of offishing Patraspractices 2, Greece ) EBFMtuna-October 15, 2012 10 / 19
Effects on Length Depth effect G.Tserpes 1, P.Peristeraki 1, C.Koutsikopoulos 2 (HCMR 1 Effects, Univ. of offishing Patraspractices 2, Greece ) EBFMtuna-October 15, 2012 11 / 19
Effects on Length by month Depth effect by month G.Tserpes 1, P.Peristeraki 1, C.Koutsikopoulos 2 (HCMR 1 Effects, Univ. of offishing Patraspractices 2, Greece ) EBFMtuna-October 15, 2012 12 / 19
Effects on Length Month G.Tserpes 1, P.Peristeraki 1, C.Koutsikopoulos 2 (HCMR 1 Effects, Univ. of offishing Patraspractices 2, Greece ) EBFMtuna-October 15, 2012 13 / 19
Probability of juvenile captures Effect of Depth, Temperature, Time, Moon phase and Month on the probability of capturing juvenile swordfish ( 100cm LJFL) GAM modelling (stepwise approach) Final model (binomial error): LJFL = Temperature + s(depth) G.Tserpes 1, P.Peristeraki 1, C.Koutsikopoulos 2 (HCMR 1 Effects, Univ. of offishing Patraspractices 2, Greece ) EBFMtuna-October 15, 2012 14 / 19
Modelling results: Juveniles G.Tserpes 1, P.Peristeraki 1, C.Koutsikopoulos 2 (HCMR 1 Effects, Univ. of offishing Patraspractices 2, Greece ) EBFMtuna-October 15, 2012 15 / 19
Effects on probability of juvenile captures Depth effect G.Tserpes 1, P.Peristeraki 1, C.Koutsikopoulos 2 (HCMR 1 Effects, Univ. of offishing Patraspractices 2, Greece ) EBFMtuna-October 15, 2012 16 / 19
Effects on probability of juvenile captures Month effect G.Tserpes 1, P.Peristeraki 1, C.Koutsikopoulos 2 (HCMR 1 Effects, Univ. of offishing Patraspractices 2, Greece ) EBFMtuna-October 15, 2012 17 / 19
Conclusions Independently of season, the setting depth of the longline seem to affect the size of the captured swordfish individuals.tserpes 1, P.Peristeraki 1, C.Koutsikopoulos 2 (HCMR 1 Effects, Univ. of offishing Patraspractices 2, Greece ) EBFMtuna-October 15, 2012 18 / 19
Conclusions Independently of season, the setting depth of the longline seem to affect the size of the captured swordfish individuals The size of the captured swordfish is positively related to the setting depth of the longline.tserpes 1, P.Peristeraki 1, C.Koutsikopoulos 2 (HCMR 1 Effects, Univ. of offishing Patraspractices 2, Greece ) EBFMtuna-October 15, 2012 18 / 19
Conclusions Independently of season, the setting depth of the longline seem to affect the size of the captured swordfish individuals The size of the captured swordfish is positively related to the setting depth of the longline The probability of capturing swordfish juveniles is inversely related to the setting depth of the gear, being generally lower in depths over 20m.Tserpes 1, P.Peristeraki 1, C.Koutsikopoulos 2 (HCMR 1 Effects, Univ. of offishing Patraspractices 2, Greece ) EBFMtuna-October 15, 2012 18 / 19
Conclusions Independently of season, the setting depth of the longline seem to affect the size of the captured swordfish individuals The size of the captured swordfish is positively related to the setting depth of the longline The probability of capturing swordfish juveniles is inversely related to the setting depth of the gear, being generally lower in depths over 20m Further experiments are needed to confirm the above findings G.Tserpes 1, P.Peristeraki 1, C.Koutsikopoulos 2 (HCMR 1 Effects, Univ. of offishing Patraspractices 2, Greece ) EBFMtuna-October 15, 2012 18 / 19
G.Tserpes 1, P.Peristeraki 1, C.Koutsikopoulos 2 (HCMR 1 Effects, Univ. of offishing Patraspractices 2, Greece ) EBFMtuna-October 15, 2012 19 / 19