757 



Survival rates for rays discarded by the 



bottom trawl squid fishery off the Falkland Islands 



Vladimir V. Laptikhovsky 



Falkland Islands Government Fisheries Department 



P.O. Box 598 



Stanley, FIQQ 1ZZ 



Falkland Islands 



E-mail address: vlaptikhovskyigfisheries.gov fk 



Waters off the Falkland Islands are 

 subject to a specialized multispecies 

 ray fishery and were first fished by 

 a Korean fleet in 1989. More than 

 twenty different rajid species have 

 been recorded from catches around 

 the islands, and five species accounted 

 for 87.04% of the total catch during 

 1993-2002. Catches peaked in 1993 

 at 8523 metric tons, and specific fish- 

 ing licenses — R (second season) and F 

 (first season) — were first introduced 

 in 1994 and in 1995, respectively 

 (Agnew et al. 2000; Falkland Islands 

 Government, 2002; Wakeford et al., 

 in press). 



In addition to the licensed ray fish- 

 ery, rays are taken as bycatch in the 

 bottom trawl fishery that targets the 

 squid Loligo gahi and, to a lesser ex- 

 tent, by the trawl fishery that targets 

 finfish. A 10% bycatch of nontarget 

 species is allowed in both these fish- 

 eries. In 2000-2002, the reported 

 ray bycatch of trawlers not licensed 

 to catch rays represented between 

 20.2% and 31.9% of the total ray 

 catch. However, under-reporting of 

 elasmobranch bycatch is a common 

 practice for trawl fisheries where 

 sharks and rays are discarded (Ste- 

 vens et al., 2000), and the reported 

 chondrichthyan catch is only about 

 half of the estimated actual global 

 catch (Bonfil, 1994). The actual ray 

 bycatch in Falkland waters may be 

 much higher than reported because 

 only large rays are processed (and 

 therefore, reported) onboard trawl- 

 ers. This situation makes ray fishery 

 management in the Falkland Islands, 

 which is already difficult because of 

 the nature of the multispecies tar- 

 get, even more complicated. However, 



good management is of primary im- 

 portance because sharks and rays 

 appear to be particularly vulnerable 

 to over-exploitation because of their 

 late attainment of sexual maturity, 

 long life span, both low fecundity and 

 natural mortality, and close relation- 

 ship between recruitment and paren- 

 tal stock (Stevens et al., 20001. In 

 the Falkland trawl fisheries (which 

 includes most trawlers licensed to 

 catch rays), rays smaller than ap- 

 proximately 30 cm disk width are 

 discarded after spending between 5 

 min and 4 hours in the fish bin and 

 passing through the factory sorting 

 line together with other catch. Some 

 rays that have been caught, stored, 

 and then discarded still show signs 

 of life. In contrast to other marine 

 organisms whose survival after be- 

 ing discarded has been investigated, 

 ray survival has been studied only 

 in Australian waters (Stobutzki et 

 al.. 2002). The aim of this study was 

 to investigate the survival rates of 

 discarded rays onboard trawlers in 

 the Falkland waters. 



Materials and methods 



The research was conducted onboard 

 the Falkland Islands registered 

 trawler Sil (length of 78.5 m, gross 

 tons (GRT) of 2156 t, net tons (NT) 

 of 647 t). The vessel used a bottom 

 trawl with a vertical opening of 5 m, 

 horizontal opening of 30 m, and a 

 codend mesh size of 110 mm. Trawl- 

 ing speed varied between 3.8 and and 

 4.2 kn. Fishing occurred at a depth 

 of 80-190 m during the day and the 

 early part of the night. The surface 



temperature was 8.7-9.2°C; the near 

 bottom temperature was 6.8-7.6°C. 

 Up to four hauls occurred daily. Each 

 catch was released from the codend 

 into the fish bin, which had a continu- 

 ous supply of sea water, and the catch 

 immediately began to be sorted on a 

 conveyor belt. Squids and commercial 

 fish were separated from the noncom- 

 mercial discarded bycatch and were 

 frozen. Of a total of 4306.2 kg of rays 

 caught during the observed period, 

 67.0% were discarded and only the 

 large rays were processed. The time 

 taken to sort the catch was between 

 1 and 3 hours. 



A total of 66 rays that had been 

 discarded by fishermen were sampled 

 randomly from the conveyor belt and 

 put into a 40-liter (44x35x26 cm) 

 or a 60-liter (31x76x26 cm) fish box 

 that contained running seawater. 

 For each animal, the species and sex 

 was identified and total length (TL) 

 and disk width (DW) were measured 

 within 1 cm. Their "stamina index" 

 was assigned according to four major 

 categories: 



A alive, flapping wings. 



I immobile, but alive, reacting to 

 irritation, spiracles beginning 

 to work actively after being 

 placed in seawater. 



D dead; immobile, but spiracles begin 

 to move slowly and irregularly 

 after being placed in seawater. 



DD dead; paralyzed, body stiffened 

 and wings curved but may 

 resume breathing after being 

 placed in seawater. 



Each ray (including those evident- 

 ly dead) was kept in these boxes ei- 

 ther until its death was evident (no 

 breathing) or it fully recovered and 

 began to try to swim actively. In 

 some rays the rate of spiracle con- 

 tractions was episodically recorded. 



Manuscript submitted 5 June 2003 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 30 June 2004 by the Scientific Editor. 



Fish. Bull. 102:757-759 (2004). 



