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 fishing 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)

Laptikhovsky, Vladimir V.

Aquatic Commons

757
Waters off the Falkland Islands are 
subject to a specialized multispecies 
ray fishery and were first fished by 
a Korean f leet 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, 
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: vlaptikhovsky@fisheries.gov.fk
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).
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., 2000). 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 (44 × 35 × 26 cm) 
or a 60-liter (31 × 76 × 26 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.
758 Fishery Bulletin 102(4)
Table 1
Species composition and survival of sampled rays. DW= disk width.
Species n TL, cm DW, cm Time spent in fish bin (min.) Survival rate (%)
Bathyraja albomaculata 14 36−61 26−44 20−110 (mean 45) 71.4
B. brachiurops 11 15−67 9–49 31–145 (mean 72) 54.6
B. griseocauda 3 62−83 47–60 30–75 (mean 60) 0.0
B. macloviana 2 36−42 24–29 70–135 0.0
B. magellanica 5 30−44 20–30 50–125 (mean 90) 60.0
Bathyraja sp. 16 24−104 21–74  5–120 (mean 52) 75.0
Psammobatis sp. 15 29−47 18–33 30–200 (mean 98) 60.0
Table 2
Ray survival (S%), mean recovery time (RT, min.), and occurrence of the four “stamina index” categories after different periods 
of time (T, min.) spent in the fish bin. T=time (minutes). A=alive; I=immobile; D=presumed dead; DD=dead.
 Occurrence of categories (%)
T n S RT A I D DD
 5−30 16 87.5 38.2 18.75 25 18.75 37.5
 31−60 20 75.0 55.5 10.0 30.0 40.0 20.0
 65−120 24 41.7 102.2 0 20.8 50.0 29.2
125−200 6 16.7 201 0 16.7 83.3 0
1 Only one individual (Psammobathis sp.).
Results
The sampled rays belonged to eight species (Table 1). Of 
the 66 sampled rays, a total of 21 were dead at sampling, 
four recovered breathing but then died, and 39 survived. 
Two rays recorded as category DD in the “stamina 
index” were released before full recovery after being held 
for 4 to 9 hours in running water. Even though these 
individuals were still breathing, both were considered 
dead because they still had stiffened bodies and curved 
wings. If they had been in such a state for a long time 
in their natural habitat, they almost certainly would 
have been consumed by scavengers or caught again by 
another trawler. The overall survival rate was 59.1%, 
female survival rate was 66.7%, and male survival rate 
was 56.4%.
All five rays assigned to the “stamina index” category 
A were sampled between 5 and 30 min (mean 20 min) 
after the catch was poured into the fish bin. All five 
individuals began immediately to breathe normally and 
recovered within 5 to 20 minutes. 
Of a total of 18 rays assigned to the “stamina index” 
category I, which were sampled between 15 and 145 min 
(mean 55.7 min) after haul, 88.9% (n=16) survived. The 
breathing of these specimens at the time of sampling 
was usually slow, although occasionally normal. Spira-
cle contraction rates gradually increased from an initial 
rate of 5−15 bit/min to 25−28 bit/min for B.brachiurops 
specimens and to 35−38 bit/min for individuals of B. 
albomaculata and Bathyraja sp. Upon attaining normal 
breathing, they remained immobile, but fully recovered 
between 15 minutes and 3 hours.
The survival rate of 28 rays that were assigned to 
the ‘‘stamina index” category D was 39.3% (n=11). Of 
the remaining individuals, two rays died after 15 and 
45 minutes after being placed in running seawater and 
15 rays were dead at the time of sampling. The skates 
were sampled between 30 and 200 min (mean 84.2 min) 
after the haul. Those that survived took 5−80 minutes 
to recover normal breathing and between 15 and 315 
minutes to attain full recovery.
A total of 15 rays were assigned the “stamina index” 
category DD. However seven of them (46.7%) survived. 
These individuals were sampled between 20 and 115 
minutes (mean 63.9 min.) after the haul and fully re-
covered within 40 to 150 minutes.
Survival rate varied substantially among the eight 
species sampled (Table 1). In general, ray survival dras-
tically decreased and recovery time increased with the 
time spent in the fish bin (Table 2). The critical dura-
tion in the fish bin appeared to be between one and two 
hours; only one Psammobathis sp. survived more than 
two hours in the fish bin and exhibited a surprisingly 
fast recovery. 
759NOTE Laptikhovsky: Survival rates for rays by the bottom trawl squid fishery
Discussion
The survival of discarded rays during trawling opera-
tions in the Falkland waters is quite important. Although 
65.2% of the individuals were initially assigned as dead, 
the actual mortality was 40.9%, although it took some 
rays up to six hours to recover. Survival of shallow-water 
shelf species such as Psammobatis sp., in particular, but 
also B. brachiurops and B. magellanica, was somewhat 
higher than relatively deep-water species such as B. 
albomaculata, B. griseocauda, and Bathyraja sp., which 
inhabit the shelf edge and upper part of the slope. This 
survival rate was most likely related to the greater 
resilience to environmental changes for shallow-water 
species, whose habitat is more changeable both season-
ally and spatially. Male survival was lower, which is in 
accordance with data for rays and skates obtained in 
northern Australian waters (Stobutzky et al., 2002).
Recent data from a tropical prawn fishery off northern 
Australia showed that on average 44% of individuals of 
a number of ray and shark species survived a trawl-
ing event (Stobutzky et al., 2002). The Falkland ray 
survival rate was higher. This difference may be due 
either to the higher metabolic rates of tropical ray spe-
cies (and therefore a higher vulnerability to asphyxia), 
or to an overestimation of their mortality, which was 
assessed immediately after individuals where landed on 
deck (unlike the recovery time allowed in the present 
study). The latter factor is more probable because in the 
present study 41.9% of rays initially recorded as dead 
(D and DD) eventually recovered.
Despite the demonstrated ability of skates to survive 
after being caught and stored in fish bins, their contin-
ued survival is not guaranteed once they are discarded. 
They may fall prey to the hundreds of albatrosses and 
other scavenging birds that are associated with trawl-
ers (author’s pers. obs.). The consumption of differ-
ent discarded fish species and squids from trawlers in 
Falkland waters by seabirds, primarily by black-browed 
albatrosses, has been studied (Thompson, 1992), but it 
is not known whether rays are also taken by sea birds 
and to what extent. Despite the great abundance of 
seabirds around vessels in the Southwest Atlantic, it 
is likely that they consume a minor part of discards as 
found in Australia (Hill and Wassenberg, 2000). Most 
of the discarded fish probably fall to the sea floor and 
attract and are consumed by bottom scavengers and 
bottom dwellers (Laptikhovsky and Fetisov, 1999; Lap-
tikhovsky and Arkhipkin, 2003). Consequently, even 
after recovering and successfully avoiding the seabirds, 
the discarded skates may be consumed or mortally in-
jured by these bottom scavengers during the recovery 
time, which appears to be about 0.5−1.5 hours.
Acknowledgments
I would like to thank the crew of FV Sil for their valu-
able help during sampling procedures and their hospital-
ity onboard; the Director of Fisheries, John Barton, for 
supporting this work; A. I. Arkhipkin and an anonimous 
reviewer for valuable comments; and Helen Otley (FIFD) 
for language editing.
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Survival rates of rays discarded by the bottom trawl squid fishery off the Falkland Islands

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Survival rates of rays discarded by the bottom trawl squid fishery off the Falkland Islands

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