Trawling Operations and South African (Cape) Fur Seals, Arctocephalus pusillus pusillus
Item Type article
Authors Wickens, Patti A.; Sims, Peter F.
Download date 06/10/2021 20:26:13
Link to Item http://hdl.handle.net/1834/26473 Trawling Operations and South African (Cape) Fur Seals, Arctocepha/us pusillus pusil/us
PAnl A. WICKENS and PETER F. SIMS
Introduction and Cawthorn, 1991). Less common are The South African (Cape) fur seal, analyses of the losses to trawl fisheries Arctocephalus pusillus pusillus, is the The incidental take of marine mam through interaction with marine mam only breeding pinniped found in south mals during trawl operations has re mals, although in South Africa this has ern Africa. This species, with a popula ceived attention in several countries, been documented and discussed (Shaugh tion size of up to 2 million seals including South Africa (Shaughnessy nessy, 1985; David, 1987; Wickens, (Anonymous, 1991), constitutes one of and Payne, 1979), Alaska (Perez and 1989; Wickens et aI., 1992). Such re the largest fur seal populations in the Loughlin, 1991), Canada (Pemberton et search has also revolved around the ex world (Croxall and Gentry, 1987). Over aI., 1994), and New Zealand (Mattlin tent of consumption of fish discarded one-third of the total population ranges by trawlers and the possibility that along the South African coastline trawler offal supports the needs of part (Wickens et aI., 1991), the area consid Patti A. Wickens is with the Marine Biology Re search Institute, University of Cape Town, of the population (David, 1987; Wick ered in this study, while the remainder Rondebosch 7700, South Africa. Peter F. Sims is ens et aI., 1992), but not on cost of the is found off the Namibian coast. Off with the Sea Fisheries Research Institute, Private Bag X2, Roggebaai 8012, South Africa. Views losses from different fisheries. All stud South Africa, seals are found at 10 or opinions expressed or implied are those of the ies of operational interactions between breeding colonies and 5 nonbreeding authors and do not necessarily represent the po seals and the trawl fishery in South Af colonies (where pups are found only on sition of the National Marine Fisheries Service, NOAA. rica (Rand, 1959; Shaughnessy and an irregular basis). The largest and only Payne, 1979; Shaughnessy, 1985; Ryan mainland colony is Kleinsee, where and Moloney, 1988; Anonymous, 1987; two-thirds of the pups in South Africa ABSTRACT-South African (Cape) fur Wickens, 1989; Wickens et aI., 1992) are born (Wickens et aI., 1991). Be seals, Arctocephalus pusillus pusillus, in have focussed on the number of seals tween 1985 and prior to the cessation teract with the South African trawl fisher attending trawling operations and the of sealing in 1990, this was the only ies-offshore demersal, inshore demersal, and midwaterfisheries. These interactions numbers entrapped in the nets, and al colony at which sealing occurred take thefollowingforms: Seals take or dam most all have dealt with offshore dem (Wickens et aI., 1991). age netted fish, on particular vessels they ersal trawling only. Wickens et al. In South Africa, the trawl fishery is become caught in the propeller, seals drown (1992) reviewed research on all seal the second largest contributor, after the in the nets, live seals come aboard and may fisheries operational interactions in pelagic purse-seine fishery (28%, an be killed. Except in specific cases of seals damaging particular trawler propellers, in South Africa, and this was followed by average of 172,000 metric tons (t) an teractions result in little cost to the offshore an evaluation of these interactions in nually between 1988 and 1992 inclu and midwater trawl fisheries. For the in South Africa (Wickens, 1993, 1994). sive), to the South African fishing in shore fishery, seals damage fish in the net Based on that study, this paper evalu dustry in tenns of the cleaned (mainly at an estimated cost in excess of R69, 728 (US$18, 827) per year, but this is negligible ates the operational interactions be headed and gutted) mass of fish landed. (0.3%) in terms ofthe value ofthe fishery. tween seals and each of the three trawl However, it is by far the largest (51 %, Seal mortality is mainly caused by drown fisheries (offshore demersal, inshore an average of R260 million or US$74 ing in trawl nets and ranges from 2,524 to demersal, and midwater) separately, in million) in tenns of financial value to 3,636 seals ofboth sexes per year. Between tenns of financial cost to the industry the industry (data from Sea Fisheries, 312 and 567 seals are deliberately killed annually, but this most likely takes place (from catch losses, gear damage, and Cape Town). Within the fishing indus only when caught and they enter the area operational disturbance) and mortality try this sector involves the largest num below deck, where they are difficult to re or injury to the seals (through inciden ber of personnel (almost 9,000), one move, and pose a potential threat to crew tal and deliberate killing) in South Af third of whom are fishennen operating safety. Overall, seal mortality during trawl ing operations is negligible (0.4-0.6%) in rican waters. This is done by evaluat on trawlers. terms of the feeding population of seals in ing new data and by making compari The trawl sector is divided into off South Africa. sons with published studies. shore and inshore demersal trawling
56(3), 1994 1 and, since 1989, midwater trawling Midwater trawling targets mainly Observations of offshore and inshore (Fig. 1). Prior to 1991 there was also an Cape horse mackerel, Trachurus tra demersal trawling were made from both experimental demersallongline fishery. churus capensis (Crawford, 1989). commercial and research trawlers, but During that longlining, an estimated There is no total allowable catch, but to the data from the two types of vessel 5.3% of the catch was lost to seals place some limitation on the exploita are not directly comparable. The re (Wickens et al., 1992), and this was tion of this species, a maximum annual search vessel was a stem trawler which considered a significant quantity. Off catch is recommended. In 1992 there trawled for a period of 30 minutes, a shore demersal trawling provides by far were seven vessels, all stern trawlers, shorter trawl time than done by com the greatest landed mass and landed licensed for midwater trawling, but mercial vessels. Research trawls were value offish. The masses offish landed most were not exclusively involved in made using a net with a 27 mm (10.6 by the inshore demersal and midwater midwater trawling. Midwater trawling inch) mesh liner as opposed to mini trawl sectors are similar, but the value is done mainly at night. mum commercial net mesh restrictions of the inshore trawled fish is greater. of 110 mm (43.3 inches) and 75 mm Data Collection Offshore demersal trawling targets (29.5 inches) to the west and east of the two species ofCape hake, Merluccius Quantitative information through in Cape Agulhas, respectively. The two capensis and M. paradoxus, for which dependent surveys was required in sets of data were analyzed separately, there is a single total allowable catch; which observers record counts of seals with the research data being used for kingklip, Genypterus capensis, is caught and incidences of entrapment during comparison only. as a by-catch (Payne, 1989). In 1992 there trawling operations aboard commercial During 1992 observers made nine were 58 active offshore trawlers which vessels. Observers were briefed before demersal offshore trawling trips on generally fish only by day. Most are stem leaving, the completed data sheets were commercial vessels, all but one of which trawlers and a few are side trawlers. examined on their return, and any un were on stem trawlers (Table 1). The Inshore demersal trawling targets usual occurrences were cross-checked. observation period totaled some 64 days hake and the Agulhas sole, Austro Independent observations were possible at sea, during which about 600 t of glossus pectoralis, for which there are on offshore trawlers, but there were lo cleaned (mainly headed and gutted) fish species-specific total allowable catches gistical difficulties in carrying out in were caught. Observations were made (Payne and Badenhorst, 1989). King dependent observations at sea on in during 222 hauls of the net. A further klip is a by-catch, as in the offshore shore demersal and midwater trawlers. 75 days of observation took place on trawl fishery. This form of trawling is done with side trawlers, both day and night. In 1992 there were 37 trawlers Table 1.-Details of commercial and research trips undertaken to observe seal interactions during trawling op erations during 1992-93. Observations on the offshore and inshore trawlers were done by independent observ actively used for inshore trawling. ers and those on the midwater trawler by the skipper.
Trip and Duration Observed vessel Company Month (days) hauls ~ Long-line Offshore demersal • Midwaler trawl Commercial Jan.-July 64 222 o Inshore demersallrawl 1. Anemone 1& Jl Jan. 9 26 200 o Offshore demersallrawl 2. Harvest Galaxy Sea Harvest Feb. 6 30 3. Erica 1& J Feb. 10 36 4. Aloe I&J Apr. 4 15 o 150 5. Harvest Belinda Sea Harvest Apr. 5 21 o 0_ 6. Begonia 1& J May 7 23 ::::. 7. Aloe 1& J June 6 18 (/) 100 CJ> 8. Aloe 1& J July 7 21 c 9. Begonia 1& J July 10 is 32 Research c 50 Feb.-April 75 132 ."l 1. Africana Feb. 25 17 2. Africana April 25 30 o .j...L-..Lt..L...---J4-J---L+-l---4.L..---J--1 3. Africana Feb. 25 84 320 Total (12 trips) 139 354
2 Marine Fisheries Review the research vessel F.R.S. Africana in trapment and deliberate killing during "west" coast, defined as the region west 1992 and 1993, during which 131 off 16 hauls in 1993 (Table 1). A discus of Cape Agulhas, and the "south" coast, shore demersal hauls were observed. sion and quantification of the interac the region east of Cape Agulhas (Fig. Six inshore demersal trawling trips tions are also provided, based on the 2). Most offshore trawling takes place were undertaken in 1992 and 1994 data collection from the offshore dem and most seal pups are born on the west (Table I). During the 27 days spent at ersal trawl observations. coast, and likewise most observation sea, a catch of approximately 44 t of For all of the trawl fisheries, catches effort is concentrated in this region, with cleaned fish were caught on 65 hauls, are expressed in terms of landed mass, less on the south coast. By contrast al all of which were observed. Conditions and economic calculations are made most all fishing effort by inshore trawl aboard inshore trawlers did not readily using landed values from 1992, the lat ers is concentrated on the south coast, allow for accommodation of additional est available data from Sea Fisheries, and all of the observer effort was done personnel as observers. Hence, the num South Africa. The South African cur in this area, mostly within 50 miles of ber of observed commercial hauls was rency of Rands is converted to U.S. dol Mossel Bay. Midwater trawling also limited. During 50 days at sea on two lars using an exchange rate of takes place mostly on the south coast, research cruises on F.R.S. Africana dur US$0.27:R1 as of July 1994. For later with a small quantity being done on the ing 1992, records of seal activity were calculations, the total number of trawls west coast. In this region there are only made during 72 inshore demersal hauls. during 1992 is used, and consisted of two breeding colonies of seals but trawl As a result of the difficulties involved 42,374 offshore demersal trawls. 21,575 ing activity is close inshore. in obtaining observations from commer inshore demersal trawls, and 1,100 Offshore and inshore demersal trawl cial inshore trawlers and the fact that midwater trawls. ing is carried out consistently through damaged fish are not sorted at sea, a For discussion purposes, the South out the year, and observations from monitoring program was established to African coastline is divided into the commercial trawlers occurred during record seal-damaged fish in the catches at landing sites. This took place at the Irvin and Johnson (I & J) and Sea Har S vest l factories in Mossel Bay, the ma jor landing site for inshore trawlers. Estimates of damaged fish and total • Kleinsee landings were recorded by the same two 30 (65% of pups) factory production supervisors at each South Africa factory from May 1992 to April 1994. o These persons are not affiliated with the vessels from which the fish are landed • and are therefore considered to be in 32 dependent recorders. The mass of seal West coast islands damaged sole and seal-bitten kingklip (33% of pups) was recorded from a total of 991 land Mossel ings, during which time over 1,068 t of Cape Bay sole and over 133 t of kingklip were 34 Agulhas • landed. Soulh coast islands t (2% of pups) On the smaller midwater trawlers it • Inshore was not possible to obtain a berth for demersal Midwater 100 Offshore 100 an observer, and the larger vessels only 36 0 demersal make a few trips during which rnidwater 80 80 l\lII o~ trawling may take place. For this rea _!!1 1l>:: 60 60 ~ ~ ~ .~ "'.:: son no independent observation data of Offshore J!!u ~ ~ 40 ~ ~ E demersal 40 a5 seal interactions with the midwater ~ ., rf i5 20 ., "' trawl fishery were obtained. However, 38 Inshore 20 a. -g " demersal one of the larger trawling companies o o chose one of their skippers as an appro West of Cape Agulhas East of Cape Agulhas llwest coast" "south coast" priate and reliable person for collect ing data. Observations were made by 14 16 18 20 22 24 26 E this skipper as some indication of en- Figure 2.-Dislribution of commercial (1992) and observed (1992-94) trawls for the off shore and inshore demersal and midwater trawl fisheries. The location of the breeding (dot) IMention of trade names or commercial firms and non-breeding colonies (circle) of the South African (Cape) fur seal in South Africa are does not imply endorsement by the National shown with the percentage of all pups born in South Africa for Kleinsee and the islands to the Marine Fisheries Service, NOAA. west and east of Cape Agulhas.
56(3),1994 3 the first half of the year when berths and number of seals counted when the the observers were likely to move be observers were available. Midwater codend of the net surfaces is taken as tween these trawlers. The size of seals trawling also occurs through the year, the average number feeding. However, is difficult to estimate but only medium but concentrated effort depends on the these counts of the actual number that (40-100 kg; 88-220 pounds) and large availability of fish and the allocated may be pulling fish from the net are a (~100 kg; ~220 pounds) seals were re quotas. Observations ofrnidwater trawl minimum, because seals will also be ported. This was expected because ing were made by the selected vessel at feeding below the surface and will not young, small seals are less likely to feed midyear. be counted. Seals counted are likely to far from the coast. move between different trawlers work The following two points regarding Seal Attendance ing in an area, and therefore this num offshore demersal trawling are noted, Seal counts were made by observers ber cannot be multiplied up by the num and both are postulated, based on our at commercial offshore and inshore de ber of trawlers to establish total num knowledge of seal distribution and mersal hauls; they include seals around bers of seals feeding in an area. behavior: the trawler, i.e., not only at the stem or First, more seals attend offshore Offshore Demersal Trawling side where the net was hauled. No trawling operations on the west coast counts of seals were made during Seals were seen on the majority than on the south coast. On the south midwater trawling. Fish processing and (>84%) of observed offshore demersal coast, offshore trawlers are restricted discard release take place throughout hauls and more frequently on the west from trawling in water <110 m «360 the trawling process, so seal attendance coast. On both the west and south feet), and this includes the Agulhas includes seals that are feeding on such coasts, it was most common for observ Bank which extends 180 n. mi. offshore discards. For offshore trawlers it is as ers to see :55 seals/haul, but on the west in places. On the west coast trawling sumed that the number of seals attend coast many more were also seen on oc takes place closer inshore and it is there ing side trawls is the same as at stem casion (Fig. 3). If the maximum num fore more accessible to the seals. The trawls, so these data are combined. ber seen during a haul is considered, observations show a mean of 18 seals The numbers of seals counted dur most observations were of 11-20 seals (with a maximum of 260) on the west ing different stages of the trawl are at a trawl on the west coast and fewer coast and a mean of 3 (with a maximum shown in Table 2. Seals are most likely on the south coast. On 40% of the ob of 10) on the south coast; this differ to take fish from the time the net nears served commercial trawls, other trawl ence is significant (Kruskal-Wallis test the surface until it is hauled aboard. The ers were visible and the seals seen by statistic =35.7, P Table 2.-0bserved number of seals around offshore and inshore demersallrawl ers during different stages of a trawl. No counts were made from midwater trawlers. Offshore demersal The minimum count in each case was zero. 40 Number of seals observed West coast Stage of trawling operation Mean ± 1 S.E. Max. 20 Offshore demersal West coast Commercial (n = 185) en 0 Trawling (Shooting to net at depth) 4 ± 0.74 90 c Start hauling net 15 ± 2.28 240 0 80 Otterboards on vessel 16 ±2.13 260 .~ South coast Codend suriaces 18 ± 2.06 260 Net aboard 18 ± 1.84 200 Q)c: Mean: Hauling to net aboard 16 ± 1.99 260 en 40 Mean number .D o Research (n = 102) 0 Codend suriaces 2 ± 0.40 30 lIB Maximum number '0 0 South coast Q) Commercial (n 37) OJ = CO Trawling (Shooting to net at depth) O±O 1 C 60 Inshore demersal Start hauling net 1 ± 0.16 5 Q) Otterboards on vessel 2 ± 0.33 10 ~ Codend suriaces 3 ± 0.33 8 Q) Net aboard 3 ± 0.33 9 a.. 40 Mean: Hauling to aboard 2 ± 0.33 10 Research (n = 30) Codend suriaces 1 ±0.37 6 20 Inshore demersal Commercial (n =65) Trawling (Shooting to net at depth) 2 ± 0.52 22 o Start hauling net 2 ± 0.39 15 1-5 6-10 11-20 21-30 31-50 51-100 >100 Otterboards on vessel 4 ± 0.52 22 Codend suriaces 7 ± 0.77 27 Net aboard 10±1.16 30 Number of seals observed during a haul Mean: Hauling to aboard 6 ± 0.90 30 Research (n = 72) Figure 3.-Numbers of South African fur seals observed at off Codend suriaces 2 ±0.24 10 shore and inshore demersal trawling operations in South Africa. 4 Marine Fisheries Review and Payne (1979) recorded differences medium (40-100 kg; 88-220 pounds) an average trawl time of 2.2 hours. The of a mean of 6 seals on the west coast and large (~ 100 kg; ~ 220 pounds) seals time of 2.1 hours observed from the net and 4 on the south coast during com were reported, although a few small depth to the start of hauling, as recorded mercial trawling. Data from research «40 kg; 88 pounds) seals were also from observations (Table 3), therefore trawls indicate double the number of seen. It is probable that the presence of indicates that the observed trawls were seals on the west coast (2 with a maxi small seals results from the proximity probably typical of offshore trawling. mum of 30) compared to the south coast of trawlers to the coast, where younger While seals may eat large quantities (l with a maximum of 6). Other counts seals are found. of fish near the net (one seal was ob of seals from research trawls that have As with offshore trawling, signifi served eating 24 free-floating fish), been documented are: on the west coast, cantly more seals accompany the in fish damage attributable to seals in off 8 (Ryan and Moloney, 1988) and 10 shore trawlers from the time the net shore-trawled catches is considered (Shaughnessy and Payne, 1979); and, starts being hauled than when the ves negligible. on the south coast, 3 seals (Shaughnessy sel is trawling (Wilcoxon test statistic Inshore Demersal Trawling and Payne, 1979). Fewer seals are seen = 5.29, P 56(3),1994 5 Figure 4.- South African fur seals feeding at an offshore demersal trawl net. Many seals may feed from the net, particularly on the west coast of South Africa (top; photo by P. Bibb), however fewer are fre quently seen (bottom; photo by J. Enticott). 6 Marine Fisheries Review . - Table 3.-0bserved duration in minutes of different stages of offshore and inshore Sole 1.2 160 demersal trawls. The difference in the time taken between the codend reaching the surface and the net being aboard is given separately for stern and side offshore ~ c 120 trawlers. 0.8 ,.. ~ j\ ...... Duration (minutes) ." • . I . ,..-,/ 1\ -. r-.. 80 i e Stage of trawling operation Mean ± 1 S.E. Min. Max. • • Offshore demersal (n = 222) 49 58 67 ~l 59 63 64 58 67 49 58 45.R Shooting net -> net at depth 21 ± 0.47 3 60 Net at depth -> start hauling net 123 ± 2.62 37 305 0 Start hauling net -> doors on vessel 14 ± 0.47 5 70 Kingklip • Otterboards on vessel -> codend surfaces 5 ± 0.20 1 34 • 20 12 Cod end on surface -> net aboard (stern. n = 192) 5 ± 0.22 1 15 • Cod end on surface -> net aboard (side, n = 30) 18± 1.28 10 43 • 15 Total: Start hauling to net aboard 25 ± 0.74 2 85 8 10 Total' Duration of trawl 171 ± 2.89 74 372 • • 4 • • Inshore demersal (n = 65) • • • 5 Shooting net -> net at depth 9 ± 0.39 1 15 Net at depth -> start hauling net 210 ± 7.62 110 335 o Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Start hauling net -> doors on vessel 10 ± 0.39 5 15 Otterboards on vessel -> codend surfaces 6 ± 0.26 3 15 Cod end on surface -> net aboard 8 ± 0.65 4 25 Figure 5.-Monthly inshore demersal trawl landings and the quan Total : Start hauling to net aboard 23 ± 0.90 15 45 tities of sale and kingklip that are seal-damaged, as recorded from Total: Duration of trawl 242 ± 7.36 140 359 two factories in Mossel Bay during this study. The numbers indi cate the number of landings examined. most commonly marketed with the head trimming. On average, 11.7% of the tionally less of the catch is available to on, so seal-damaged fish which may be catch was damaged by seals which is a the seals. Spoilage of fish is therefore missing a portion of the body and head loss of 3.9% of the mass prior to land considered to be negligible. (Fig. 6a) are sold for a lower price per ing. Although the 1992 landings were Equipment Damage unit mass. The reduction in price of a 200 t, the potential landing, if no seal damaged fish depends on the initial size damage had occurred, could have been Net damage by seals is not generally of the fish, because prices per fish are 208.1 t, providing an estimate of dam considered to be a problem during any size-dependent. On average, sole were aged kingklip at 8.1 t. At the 1992 form of trawling. Observers did note, considered to be reduced in price by landed price of R5.76(US$1.56)/kg, as a matter of course, the damage to 50%, although the vessels sometimes some R46,656 (US$12,597) would be fishing gear resulting from various kept the seal-damaged sole to sell else lost because of seals. causes, but only on an offshore trawler where at a higher price. At least 5.6 t Overall the loss through seal depre was minor net damage caused by a seal (0.7%) from the 1992 landings (797 t) dation of sole and kingklip is calculated when it attempted to free itselffrom the were estimated to be seal-damaged, al as R69,n8 (US$18,827). This does not net (0.5% of offshore trawls). Both off though this is an underestimate because include fish that are pulled through the shore and inshore demersal nets were whole sole may be pulled from the net net mesh by seals and lost (particularly occasionally tom during observations, by seals and not recorded at the factory in the case of sole which can be pulled either from dragging on the bottom or amongst the damaged fish. The landed from the net whole), damage to other from rocks that were brought up. The price of sole in 1992 was R8.24 species, or damaged fish that are not size of the tears varied, as did the time (US$2.22)/kg. If this damaged mass landed. It can therefore be regarded as taken to repair them. were sold at half price then the loss a minimum. The propellers of some offshore de would be R23,On (US$6,229). mersal trawlers are mounted in Kort Midwater Trawling Kingklip damage varied between 4.4 nozzles which increases suction. Seals and 15.3% of the landings and was no Midwater trawls may last from about feeding beside such vessels can be ticeably lower in February and Novem 10 minutes to a few hours, depending sucked into the nozzle and damage the ber/December, but the reasons for this on depth and visibility of the fish; they propeller by bending or breaking off a are not known. Kingklip is marketed in averaged 2.6 hours during the observa part, and this may be costly. A trawler various forms so seal-damaged fish tions in this study. The smaller mesh of with a damaged propeller increases fuel (Fig. 6b) is only regarded as a loss of the midwater trawl net means that less consumption of the vessel, requires in mass, not a loss in the price per unit of the entrapped fish protrude, and they spection by a diver, and may require mass. For kingklip it is assumed that a are therefore not easily accessible to repair or replacement. At least one-third third of the mass of each damaged fish seals. The larger catches made by of the vessels owned by the two major is lost as a result of the seal bite and midwater trawlers mean that propor trawling companies are fitted with Kort 56(3),1994 7 Figure 6.-Seal-damaged sole (a) and kingklip (b) from the inshore demersal fishery. Photo a by P. Sims and Photo b by L. Taylor. nozzles, but few complaints of seals have finely mincing the discarded fish so that which live seals were brought aboard. been made by skippers. We suggest that it is less attractive for seals. In this way In eight of these, one seal was involved, problems may be related to the specific it is hoped that seals will not feed near and in the remaining three there were design of the vessel or to the position of the offal outlet and therefore will be less two seals. These incidents involved a the offal outlet at which seals may feed. likely to be sucked into the nozzle. From total of 14 seals, averaging 7.6 seals per Two I & J trawlers, in particular, have the trials carried out to date, the experi 100 hauls. In two of the incidents a seal reported such problems, and In 1991 ment has proven successful. managed to get below deck (1.1 % of both had the factory deck layout rede hauls). In one case, fish boxes were Live Seals Aboard signed to move the outlet for discarded placed strategically to provide the seal fish away from the propeller. In each Fishing operations may be disrupted with an escape route and it climbed out case, the cost was about one million if live seals are brought aboard in the and left the vessel after about 90 min Rand (about US$250,000). However, net. Generally, returning live seals to the utes (Fig. 7). In the other case, the seal the problem was not resolved and ob sea is not a problem and, from observa became trapped in the factory area, and servers present during three trips on tions, in most instances the seals left the it was clubbed to death after removal these vessels heard a thud and the engine vessel of their own accord or were attempts failed. straining as a seal passed through or be chased out by the crew. Most seals On the 37 observed south coast hauls came stuck in the nozzle. On some occa brought aboard do not go below deck, there was one incident (2.7% of hauls sions there was blood in the water and but when this happens it can be a prob average) of a single seal coming up in injured seals surfaced. On one trip, the lem. Nevertheless, injuries resulting from the net. The time taken for the seals on auxiliary power had to be brought in to seals aboard trawlers are not common. deck to leave the vessel generally var complete the trawl and the main engine ied from almost immediately to 45 min Offshore Demersal Trawling was then reversed to release a dead seal. utes. An exceptional case was of a seal In late 1992, one of the I & J vessels During the 185 offshore demersal which was thought to be injured taking which had problems with seals was fit trawls observed on the west coast, there over 5 hours to leave, having been ted with a "crusher" to experiment with were 11 incidents (5.9% of hauls) in brought aboard during the last haul of the 8 Marine Fisheries Review hauls, or 1.6 seals per 100 hauls. In each case it was a single seal per haul, two of the seals being female and one male, ranging in size from 1.4 to 1.7 m. The three drownings took place on clear days and were in different areas; the car casses were dumped overboard. In New Zealand, seals drown predominantly dur ing night trawling (Anonymous, 1990). Based on the annual number of off shore demersal hauls in each area, the total number of drownings would be 498 per year, possibly in the ratio of 332 females to 166 males, an overall aver age of 1.2 seals per 100 hauls. By com parison, one seal of unknown sex was drowned during research trawls on the west coast, i.e., 0.8 seals per 100 hauls. Shaughnessy and Payne (1979) indicate a greater drowning frequency than ob served during this study, namely 3.8 seals per 100 hauls (no sex differentia tion is given), which totals 1,610 seals drowning per year based on the num Figure 7.-A seal caught in the hold of an offshore demersal trawler. [n this case the crew ber of trawls during 1992. placed fish boxes in the hold and the seal climbed out and left the vessel via the stem. Photo by J. Enticot!. Inshore Demersal Trawling The only form of seal mortality ob day. No live seals were brought aboard caught in the net than in other trawl nets. served on inshore demersal trawlers was during the 131 research trawls observed. During the 16 midwater hauls observed through incidental drowning. While live Based on the number of commercial by a skipper, there were a total of 20 seals brought aboard may be killed de trawls on the west coast (31,178) and live seals aboard in 10 of the hauls. This liberately if considered a risk to the the south coast (11,196) during 1992 amounts to an occurrence of live seals crew, there are no data on this. During and the observed percentage of times on 63% of hauls or 693 incidences per observations, there were three incidents live seals were brought aboard in each year. This averaged 1.25 seals per in which seals were drowned in nets, area, a total of 2,672 seals are estimated midwater haul or 1,034 seals per year an average of 4.6 seals per 100 hauls. to come aboard in a year (6.3 seals per with a maximum of 4 seals in anyone All were male and ranged in size be 100 hauls). This is about 46/vessel an haul. Ofthese seals, 2 (10%) were killed tween 1.2 and 1.4 m, and all three were nually. In comparison, Shaughnessy and because they entered the area below deck, caught during the day. The annual inci Payne (1979) reported a seal brought making it difficult to remove them. dence of drownings, estimated from the aboard in 3.3% oftrawls, i.e. 1,398 live total number of commercial hauls, was Incidental Seal seals brought aboard during the num 992 seals, possibly all male. ber of trawls made in 1992. Mortality or Injury Incidental killing includes seals be Midwater Trawling Inshore Demersal Trawling coming caught in Kort nozzles and The wider opening of the midwater Although no live seals were taken killed by the propeller as well as seals trawl net, as opposed to a bottom trawl aboard during any of the inshore dem drowning in nets. net, allows more seals to be caught. The ersal trawls observed (commercial and slower retrieval, lower buoyancy, and Offshore Demersal Trawling research), they are known to get aboard tendency to trawl until the net reaches but never to the areas below deck. On one observation trip on offshore the vessel mean that more seals drown Therefore they are hardly ever a prob trawlers, at least eight seals may have been than during bottom trawls. It is possible lem to return to the sea. killed by the propeller, as identified by that, as a result of midwater trawls be blood in the water and the straining of the Midwater Trawling ing done at night, more seals may be engines as the seals were entrapped. caught, as occurs in New Zealand The mouth of a midwater trawl is During offshore demersal trawling, (Anonymous, 1990). wider than that of a demersal trawl, and seals drowned in the nets on the west During the trip on which the skipper consequently more seals are likely to be coast only. In total, 3 drowned in 185 recorded seal occurrences in 16 mid 56(3), /994 9 water hauls, there were a total of 15 Inshore Demersal Trawling Summary of Interactions drowned seals on 10 (63%) of the hauls, No live seals were brought aboard The extent of the interactions be an average of 94 seals per 100 hauls. during the 65 observed trawls. However, tween seals and the three trawl fisher One or two seals were drowned during it may occur and the seals may then be ies in South Africa differ (Table 4). In each of these 10 hauls. killed. the offshore demersal trawl fishery, During a limited set of previous ob seals appear to cause few problems servations, in all, 16 dead seals were Midwater Trawling technically or financially. Some two observed in 4 commercial midwater Based on the observations made by thirds of the offshore demersal catch is trawls, averaging 4 per trawl (Wickens the skipper during 16 hauls, 2 seals went made on the west coast of South Africa et aI., 1992). On the F.R.S. Africana, below deck and were killed by the crew. where most of the seals are found. The large numbers of seals have been caught The sex of the seals was not recorded. average number of seals attending off in pelagic research trawls at night, and This amounts to an occurrence of 10% shore trawling operations in this area is on at least two occasions there have of live seals aboard being killed, or 13 18, but the average is even lower on the been incidents west of Cape Agulhas in seals per 100 midwater hauls. Based on south coast. Propeller damage, which which many seals were caught. On one the 1992 number of midwater trawls, has in the past been costly, occurs on day, in an II-minute drag, 28 seals were this would amount to 143 seals/year. only a few vessels, and ways to allevi- drowned in the net. On another day, during a 20-minute drag, between 25 and 30 seals were caught, most of which were still alive. Those numbers of seals Table 4.-Summary 01 interactions that occur between seals and ollshore and inshore bottom trawling and seen caught are, however, uncommon midwater trawling activities with estimates of cost to the fishery and seal mortality. in pelagic research trawls. Demersal trawling Based on the number of drownings Midwater observed (0.94/trawl, for the skipper Item Offshore Inshore trawling data, or from a select number of com Seal attendance around vessel Frequency >84% of hauls 95% of hauls mercial hauls, 4/trawl), a probable num Mean <18 <10 ber of 1,034 drowned seals, or a maxi Maximum 260 30 mum estimate of 4,400 drownings per Effect on fishery year, is likely. Midwater trawling is a Fish spoilage Negligible >R69,728 Negligible' Net damage (tears) relatively new fishing method, but mor Frequency 0.5% of hauls o 0' Type Small tears tality could increase if the midwater Annual cost Negligible Negligible2 Negligible'.2 trawl fishery increased and if it ex Propeller damage ?' o o Live seals aboard panded up the west coast where seals Frequency 6.3 (3.34) sealsll00 hauls 0' 1.25 sealsll00 hauls 4 are more abundant. Annual total 2,672 (1,398 ) sealslyr 0' 1.034 sealslyr Annual cost attributable to seals Negligible' >R69.728 Negligible 1.2 (US$18.827) Deliberate Seal Landed value of fishery (1992) R182.799.000 R20,930,000 R6,461 ,000 Mortality or Injury (US$49.356.000) (US$5,651.000) (US$1.744,000) Percentage of landed value lost to Deliberate killing may take place if seals (1992) Negligible' >0.3% Negligible'·2 live seals are brought on deck, cannot Effect on seals Incidental mortality be removed, and are potentially harm Drowning 4 ful to the crew. Frequency 1.2 (3.8 ) seals/1 00 hauls 4.6 sealsll00 hauls 94 seals 1100 hauls 4 Annual total 498 (1 ,610 ) sealslyr 992 sealslyr 1,034 sealslyr In propeller ?' o o Offshore Demersal Trawling Deliberate mortality Potential risk to crew On one occasion a male seal (which Frequency 0.5 (1.04) % of hauls 0' 13 sealsll00 hauls 4 Annual total 169 (424 ) sealslyr ?' 143 sealslyr was trapped below deck) was deliber 4 Annual seal mortality 667 (2.034 ) + ? ' 992 + ?' 1,177 ately killed by the crew because it may Percentage mortality from feeding 4 have injured a crew member. This oc population of 650,000 seals· 0.1 (0.3 ) + ?' 0.2 + ?' 0.2 curred on the west coast and amounts 1 By inference from a comparison of the information regarding offshore demersal trawling and differences between dem ersal and midwater trawling. to a seal being killed in 0.5% of west 2 No net damage was observed. but the cost is likely to be negligible. if it does occur. coast hauls, an average ofone seal killed 'The incidence of seals going through the Kort n02zle, damaging the propeller, and being killed occurs only on some in 0.4% of all hauls. Based on the total offshore demersal vessels and this m"¥ have been resolved. The problem is therefore excluded from the calculation of cost to this fishery. number of offshore hauls in 1992 this 4 Figure calculated from Shaughnessy and Payne (1979). is equivalent to 169 seals per year. 5 No live seals aboard were observed during the limited number of observations, but live seals are likely to come aboard Shaughnessy and Payne (1979) report a and may be killed if considered a potential risk to the crew. 6 There are insufficient data on the age and sex of seals that attend trawling operations or die as a result of their encoun· single deliberate killing per 100 offshore ter. Pups are unlikely to be on the traWling grounds so the maximum number of seals that may be encountered is the trawls (no sex given) or 424 per year based South African proportion (Wickens et aI., 1991) of the feeding population (Anonymous. 1991). From all three types of trawling. the total mortality is calculated as 2.836-4,203 seals per year. Overall this amounts to 0.4-0.6% of the feeding on the current number of hauls in 1992. population annually. 10 Marine Fisheries Review ate or eliminate the problem are being shore trawling is approximately a thou first author acknowledges the funding investigated by the company concerned. sand per year, considered a negligible received from the Sea Fisheries Re Incidental and, on occasion, deliberate loss in terms of the feeding population search Institute and the Southern Afri mortality of seals, is probably in the size. can Nature Foundation (representing the order of at most a few thousand seals No particular form of deterrent is World Wide Fund for Nature in south per year. Of the three seals that drowned considered necessary at this stage to ern Africa). The grants were adminis during observations, two were female prevent interaction of seals with off tered by the University of Cape Town, but during inshore trawling the drowned shore demersal and midwater trawlers. and logistic support was provided by the animals were all male. The observations In order to minimize damage to the Zoology Department, University of therefore do not show that there is nec catch on inshore trawlers, crews usually Cape Town. essarily any bias by sex. It is unlikely try to retrieve the net as quickly as pos Literature Cited that the number of seals dying as a re sible. Brightly colored strips of plastic Anonymous. 1987. Technical guidelines for the sult of offshore trawling operations will or canvas are sometimes also used to development of an S.P.C.A. policy on the have a noticeable negative impact on the deter the seals, but these have not been management of the Cape fur seal. Head Of total population. very effective. Trials with a device to fice, S.P.C.A., Cape Town, 14 p. ___ . 1990. Report on the fur seal-hoki fish In the inshore trawl fishery, damage eliminate the problem with seals and ery technical working group. MAFFish Rep., to fish is generally considered to be the Kort nozzles on offshore trawlers, dis 3 April 1990,25 p. only problem attributable to seals, and cussed earlier, are underway. __-=-' 1991. Report of the Benguela Ecol ogy Programme workshop on seal/fishery in it probably occurs during most hauls to Facilitation of removal of live seals teractions. Rep. Benguela Ecol. Program S. at least some degree. Inshore trawling from trawlers is possibly the only ac Afr. 22, 65 p. Crawford, R. J. M. 1989. Horse mackerels and takes place only on the south coast and tion currently required. Various meth saury.ln A. I. L. Payne and R. J. M. Crawford seals are generally present during op ods, such as those suggested for the (Editors), Oceans of life off southern Africa, erations in numbers <10. The cost of New Zealand trawl fishery, could be p. 122-129. Vlaeberg, Cape Town. Croxall, J. P., and R. L. Gentry. 1987. The 1984 the damage is believed as small in com tried. These include use of choker poles, fur seal symposium: an introduction. In J. P. parison to the landed value of the fish deck and fire hoses, and the use of nets Croxall and R. L. Gentry (Editors), Status, ery. Because the Agulhas sole market (Anonymous, 1990). biology, and ecology offur seals, p. 1-4. U.S. Dep. Commer., NOAA Tech. Rep. NMFS 51. requires the fish in gutted (but head-on) Acknowledgments David, J. H. M. 1987. Diet of the South African form, seal damage can reduce the price fur seal (1974-1985) and an assessment of competition with fisheries in southern Africa. per unit mass. With kingklip, there is a The authors are grateful to Barrie In A. I. L. Payne, K. H. Brink, K. H. Mann, loss of landed mass as a result of the Rose, Graham Brill, and Nigel Camp and R. Hilborn (Editors), Benguela trophic trimming of fish to remove seal.dam bell for making arrangements for ob functioning. S. Afr. J. Mar. Sci. 5:693-713. Mattlin, R., and M. W. Cawthorn. 1991. A re age. Incidental seal mortality by drown servers to accompany trawlers; to the view of seal-fisheries interactions in New ing is not uncommon during inshore skippers and crew from Irvin & John Zealand. In Anonymous, Report of the trawling and, though not witnessed, live son, Sea Harvest, Mariette Fishing, and Benguela Ecology Programme workshop on seal/fishery interactions. Rep. Benguela Ecol. seals aboard may be killed if the crew P. Cronje for accommodating observ Program S. Afr. 22:36-38. is believed to be at risk. The total an ers on their vessels; to the observers, Payne, AI. L. 1989. Cape hakes.ln A I. L. Payne and R. J. M. Crawford (Editors), Oceans of nual mortality of seals during inshore Jim Enticott, Keith Barnes, Christiaan life off southern Africa, p. 136-147. Vlaeberg, trawling is probably in the region of a Boix, Eric-John Harris, Kevin Hey Cape Town. thousand seals per year; again, this is denrych, Jon Mantel, Rodney Shepherd, _:::-:-_andA Badenhorst. 1989. Other ground fish resources. In A. I. L. Payne and not considered important in ternlS of the and Llewellyn Taylor, who were respon R. J. M. Crawford (Editors), Oceans of life size of the seal population. sible for interacting with the fishermen off southern Africa, p. 148-156. Vlaeberg, During midwater trawling, seals can and spending long days at sea doing Cape Town. Pemberton, D., B. Merdsoy, R. Gales, and D. probably be considered little problem observations; and to the production su Renouf. 1994. The interaction between off and, if anything, less of a problem than pervisors at the factories for collecting shore cod trawlers and harp seals, Phoca during offshore demersal trawling. Fish the information on seal-damaged fish. groenlandica, and hooded seals, Cys/ophora crista/a, off Newfoundland, Canada. BioI. in the net are less accessible than on We also thank Tom Lough~ljn (NMFS, Conserv.68:123-127. demersal trawls, so seal predation on National Marine Mammal Laboratory, Perez, M. A., and T. R. Loughlin. 1991. Inciden tal catch of marine mammals by foreign and fish in the net is negligible. Based on Seattle, Wash.) and many from the Sea joint venture trawl vessels in the U.S. EEZ of the limited number of observations, the Fisheries Research Institute, Cape the North Pacific, 1973-88. U.S. Dep. number of seals, both alive and drowned, Town, who provided invaluable advice Commer., NOAA Tech. Rep. NMFS 104, 57 p. that come aboard in the net can be con in the design and collection of observa Rand, R. W. 1959. The Cape fur seal (Arc/o sidered notable per trawl, and live seals tion data; Carlos Villacastin (Zoology cephalus pusillus). Distribution, abundance aboard that are a potential risk to the Department, University of Cape Town) and feeding habits off the south western coast of the Cape Province. Invest. Rep. Div. Sea crew are deliberately killed. However, for carrying out statistical analyses; and Fish. S. Afr. 34, 75 p. given the small number of midwater Andy Payne (Sea Fisheries Research Ryan, P. G., and C. L. Moloney. 1988. Effect of trawling on bird and seal distributions in the trawls that take place during a year, the Institute, Cape Town) for commenting southern Benguela region. Mar. Ecol. Prog. overall number dying as a result of in on and improving the manuscript. The Ser. 45: 1-11. 56(3),1994 11 Shaughnessy, P. D. 1985. Interactions between fish Ecosystem. Ph.D. thesis, Univ. Cape Town, numbers of the South African fur seal: impli eries and Cape fur seals in southern Africa. In J. 288 p. cations for management. S. Afr. J. Mar. Sci. R. Beddington, R. J. H. Beverton, and D. M. _-,--_-,. 1993. An evaluation of operational Il:307-326. Lavigne (Editors), Marine mammals and fish interactions between seals and fisheries in South _-=--=-_' D. W. Japp, P. A. Shelton, F. Kriel, P. eries, p. I 19-134. George Allen & Unwin, Land. Africa. Rep. Dep. Environ. Aff. S. Afr. 146 p. C. Goosen, B. Rose, C. J. Augustyn, C. A. R. ---7. and A. I. L. Payne. J979. Incidental __--;-_. 1994. Operational interactions between Bross, A. J. Penney, and R. G. Krohn. mortality of Cape fur seals during trawl fish seals and fisheries in South Africa. S. Afr. Dep. 1992. Seals and fisheries: competition and ing activities in South African waters. Fish. Environ. Aff.lSouth. Afr. Nat. Found., Cape conflict. In A. I. L. Payne, K. H. Brink, K. H. Bull. S. Afr. 12:20-25. Town, 162 p. Mann, and R. Hilborn (Editors), Benguela Wickens, P. A. 1989. Interactions of the South --=---;0;;---:' J. H. M. David, P. A. Shelton, and J. trophic functioning. S. Afr. J. Mar. Sci. African fur seal and fisheries in the Benguela G. Field. 1991. Trends in harvests and pup 12:773-789. 12 Marine Fisheries Review