MARINE ECOLOGY Mar. Ecol. Prog. Ser. Published September in recently A - PDF document

MARINE ECOLOGY Mar. Ecol. Prog. Ser. Published September in recently Agriculture, Fisheries Fisheries Laboratory, Benarth Conwy. Gwynedd LL32 8UB, The diets cuculus and Eutrigla gurnardus, lesser-spotted dogfish Scyliorhinus canicula and whiting amphipod Ampelisca spinipes their diets. trawling damaged purple burrowing Some mobile invertebrate scavengers, Observa- tions of the seabed side-scan sonar around the tracks than results indicate migrate into whlch have been either damaged scavenging invertebrates. areas where certain communities occur, beam such that & (present study). fishing in (Pearson main fishing methods used catch demersal (BEON unavoidable side-effect action is the gear and/or damages fragde infauna, for example burrowing heart urchins, Echino- cardium cordatum and the Arctica islandica (Bergman & Hup 1992), and also increases the epi- faunal by-catch (Creutzberg et al. 1987, Kaiser et al. 1994). The consequences of these short-term 42 Mar. Ecol. Prog. Ser. 112: 41-49, 1994 Furness 1982, Wassenberg & some species from fisheries studies have examined scavengers (but & Hill 1987), and most of the avail- able data is either circumstantial or unpublished. For example, dabs Limanda have been on trawl tracks fishing occurred (G. Fonds pers. is common recently trawled to exploit a wider programme trawling on a benthic community Eutrigla gurnardus, lesser-spotted dogfish Scyliorhinus and whiting Merlangius merlan- study was determine whether fish move into recently trawled killed or beam trawl or on immigrating scavengers. trawling was 'Corystes' Anglesey, North Wales, 1992, April 1993 April 1994. differed on other experiments incorporated into programme, hence, have treated each date occasion, a wayline plotted on fished using fitted with codend. was approximately S-'). ship's position a Sercel Differential Global Positioning System (DGPS) * navigation plotter. addition, a naviga- way- line. The beam trawl's position, using a us to determine the trawls to ~t the same as the to minimise trawl track ship's plotted Fig. 1. commercial pattern 4 m, headline length recorded every 1 s using Microplot displayed a tracks. Sediment type was 'RoxAnn', a seabed lowed a either 3 the same wayline. a disturbance effect using to collect been feeding on trawled was necessary tows to collect fish for analysis. After wayline times to collect which may was carried 09:OO and 18:OO GMT in 05:17 h, dusk 19:09 h; August: dawn 05:26 h, dusk 19:54 h GMT). Prog. Ser. * * I I Before ~fterl ., LC PAMCLO DOGFISH 3 20- a 0 $15- Q r 0 10- 5 P S z Mean number gurnards (n 60), collected both h after fishing an area with a 4 m beam trawl. Significant differences were determined using X*, *p 0.05, **p c Key to Lio- Ampelisca spinipes; Calliony- mus spp.; U, Upogebia deltaura; E, Eupagurus bernhardus; B, Buccinum undatum; PL, polychaetes; AM, Ammodytes urchin gonads; k stomach contents wet weight (g) and ness (scale 0 to 10, empty to full) gurnards Aspitrigla cuculus and Eutrigla gurnardus and dogfish Scyliorhinus canicula collected intensive beam trawling using the Kruskal-Wallis non-parametric ANOVA (H) Species Stomach contents H P Before After Contents weight Gurnards 0.98 * 2.57 1.10 * 1.20 8.47 0.004 Dogfish 7.67 * 9.15 4.06 * 4.56 3.05 0.08 Fullness Gurnards 3.36 i 3.65 5.04 i 3.23 6.83 0.009 Dogfish 4.23 i 2.80 4.63 i 3.21 0.18 0.67 of the purple heart urchin Spatanguspurpureus, fish collected from Morphometrics The mean whiting examined fishing did not significantly (Table smaller prey after wayline fished (Table pw:gw Side-scan sonar observations seabed m after tow 6. Immediately (1524 to 16:OO fish marks However, immediately (18:26 to 19:OO over both areas had respectively (Table marks (Fig. 3) 2. range (mean * SE) of gurnards Aspitrigla cuculus and Eutrigla gurnardus, dogfish Scyliorhinus whiting Merlangius collected before fishing. Comparisons were made ANOVA Species n Before After Ampelisca spinipes (x2 = 11.7, 1 Whiting 80 20.8 * 2.5 19.7 i 2.7 2.98 0.09 1 significantly after trawling (Fig. 2, X* = 5.7, p 0.0251. After the area had been trawled, whiting significantly p 0.005) and their stomachs contained the gonads L Gurnards 60 26,7 * 6,11 24,4 * 2.05 0,16 Doafish 60 55.2 * 52,2 * 6.7 3.03 0,09 Fig. 3. Po~tions showing the 4 visible in side-scan record. tracks clearly relatively smooth substrate. trawl tracks less visible in thls sections fish marks concentrated in the area simultaneously on 200m wide Ser. 112: 41-49, 1994 (e.g. mysids) are displaced. This would indicate that A. spinipes are encountered more frequently by fish after an area has been beam trawled. We observed that Liocarcinus depurator, Pandalus spp. and Crangon spp. either increased in the diet of gurnards and dogfish or were only eaten after trawling (Fig. 2). These crustaceans are mobile epibenthic scav- engers (Wassenberg & Hill 1987, Hall et al. 1990a, Hedqvist-Johnson & Andre 1991), which locate carrion by following its scent in water currents (Sainte-Marie & Hargrave 1987, Nickel1 & Moore 1992). Presumably invertebrate scavengers aggregate over trawl tracks in response to the odour of animals damaged or killed by beam trawling, where, in turn, they will be vulnerable to predation by fish. We do not attribute the observed dietary changes to die1 variations in feeding activity, as all the fishing was carried out during daytime. Moreover, we found no evidence in the published literature to suggest that gurnards exhibit diurnal feeding patterns. However, Robb (1981) showed that the mean weight of whiting stomach contents increased steadily after dusk, which approximately coincided with the beginning of our final side-scan record (18:26 h, April 1993). The sud- den appearance of fish marks on the side-scan sonar record also may be attributed to diurnal shoaling behaviour. The fish marks (presumed to be shoals of whiting) were viewed simultaneously on the side-scan sonar and on an echo sounder and were positioned within 1 m of the seabed. shows that tracks, either trawl, or on other scavengers. in a similar as one cause large-scale changes in benthic com- (Pearson 1985, Lindeboom 1990, Berg- man & some animals a result the direct trawling (e.g. benthos by- catch) other by-products which large increases certain species feeding mode The structure resource partition- 1990b), certain species that exhibit opportunistic feeding authors thank Raffaelli for constructive comments which to improve the manu- script. Reference to proprietary products in products which Arkley, K. (1991). Improved selectivity in beam trawls - an inventory of vessels and gear types engaged in beam trawling in the U.K. Seafish Industry report No. 1417, Hull, p. 1-7 BEON (1991). Effects of beam trawl fishery on the bottom fauna in the North Sea. BEON rapport No. 13. Nether- lands Institute for Sea Research, Texel, p. 1-85 Berghahn, R. (1990). On the potential impact of shrimping on trophic relationships in the Wadden Sea. In: Barnes, M,, Gibson, R. N. (eds.) Trophic relationships in the marine ecosystem. Proc. 24th Eur. mar. biol. Symp. Aberdeen Univ. Press, Aberdeen, p. 130-140 Bergman, M. J. N., Hup, M. (1992). Direct effects of beam- trawling on macrofauna in a sandy sediment in the southern North Sea. ICES J. mar. Sci. 49: 5-13 Bridger, J. P. (1970). Some effects of the passage of a trawl over a seabed. Cornm. Meet. int. Coun. Explor. Sea C.M.- ICESB: 10 Bridger, J. P. (1972). Some observations on the penetration into the sea bed of tickler chains on a beam trawl. Comm. Meet. int. Coun. Explor. Sea CM.-ICES/B: 7 Collie, J. S. (1987). Food consumption by yellowtail flounder in relation to production of its benthic prey. Mar. Ecol. Prog. Ser. 36: 205-213 Creutzberg, F., Duineveld, G. C. A., van Noort, G. J. (1987). The effect of different numbers of tickler chains on beam- trawl catches. ICES J. mar. Sci. 43: 159-168 Dauvin, J. C. (1988). The effects of macrobenthos on the feed- ing of demersal fishes living in the fine sand from western English Channel (in Morlaix Bay). Cah. Biol. mar. 29: 445-467 de Gee, A., Kikkert, A. H. (1993). Analysis of the grey gurnard (Eutrigla gurnardus) Meet. int. C.M.-ICES/G: 14 Eleftheriou, A., Robertson, M. R. (1992). The effects of ex- perimental scallop dredging on the fauna and physical environment of a shallow sandy community. Neth. J. Sea Res. 30: 289-299