Bottlenose Dolphins, Tursiops truncatus, Removing By-catch from Prawn-trawl Codends During Fishing in New South Wales, Australia

During a fishing trip to record video footage of fish escaping from a by-catch reducing device located in a commercial prawn trawl, two bottlenose dolphins, Tursiops truncatus, were observed to actively manipulate the codend at the seabed, removing and consuming components of catch (mostly juvenile whiting, Sillago spp.). The observed feeding pattern suggests a well established behavioral response to trawling activities and is discussed with respect to (1) the potential nutritional benefit that dolphins may derive from such activities and (2) the effects that scavenging may have on selectivity of the gear.

Effects of Gear Modifications on the Trawl Performance and Catching Efficiency of the West Coast Upper Continental Slope Groundfish Survey Trawl

Since 1984, annual bottom trawl surveys of the west coast (California–Washington) upper continental slope (WCUCS) have provided information on the abundance, distribution, and biological characteristics of groundfish resources. Slope species of the deep-water complex (DWC) are of particular importance and include Dover sole, Microstomus pacificus; sablefish, Anoplopoma fimbria; shortspine thornyhead, Sebastolobus alascanus; and longspine thornyhead, S. altivelis. In the fall of 1994, we conducted an experimental gear research cruise in lieu of our normal survey because of concerns about the performance of the survey trawl. The experiment was conducted on a soft mud bottom at depths of 460–490 m off the central Oregon coast. Treatments included different combinations of door-bridle rigging, groundgear weight, and scope length. The experimental design was a 2 ´ 2 ´ 2 factorial within a randomized complete-block. Analysis of variance was used to examine the effects of gear modifications on the engineering performance of the trawl (i.e. trawl dimensions, variation in trawl dimensions, and door attitude) and to determine if catch rates in terms of weight and number of DWC species and invertebrates were affected by the gear modifications. Trawl performance was highly variable for the historically used standard trawl configuration. Improvements were observed with the addition of either a 2-bridle door or lighter ground gear. Changes in scope length had relatively little effect on trawl performance. The interaction of door bridle and ground gear weight had the most effect on trawl performance. In spite of the standard trawl’s erratic performance, catch rates of all four DWC species and invertebrates were not significantly different than the 2-bridle/heavy combination, which did the best in terms of engineering performance. The most important factor affecting DWC catch rates was ground gear. Scope length and the type of door bridle had little effect on DWC catch rates. Subsequent revisions to survey gear and towing protocol and their impact on the continuity of the slope survey time series are discussed.

Observations of the 1992 U.S. Pelagic Pair Trawl Fishery in the Northwest Atlantic

Pelagic pair trawling for tuna, Thunnus spp., and swordfish, Xiphias gladius, was introduced in U.S. Northwest Atlantic waters in 1991. During autumn (October-November) of 1992 under the authority oft he Federal Atlantic Swordfish Regulations, the National Marine Fisheries Service placed observers aboard pelagic pair trawl vessels to document the catch, bycatch, discard, and gear used in this new fishery. The fishery is conducted primarily at night along shelf-edge waters from June to November. In late 1991, revised regulations restricted swordfish to bycatch in this fishery resulting in pelagic pair trawl vessels targeting tuna throughout 1992. Analyses of 1992 data indicate that albacore, T. alalunga, was the predominant species caught, although yellowfin tuna, T. albaeares, and bigeye tuna, T. obesus, were the preferred target species. Bycatch also included swordfish, large sharks, pelagic rays and other pelagic fishes, other tunas, and marine mammals.

The By-catch From the Artisanal Shrimp Trawl Fishery, Gulf of Paria, Trinidad

Samples of shrimp trawl catches were collected from a commercial artisanal vessel fishing inside the 6-fm isobath in the Gulf of Paria, Trinidad. From August 1986 to May 1987, 34 late evening-early morning trawl trips were made and 97 hauls were sampled. Annual ratio estimates were 9 (SD 1.3) finfish:shrimp and 14.7 (SD 2.0) by-catch: shrimp, with the highest ratios observed August through December and the lowest from late January through May, the dry season. Extrapolation of ratios, using shrimp catch statistics, indicates that for 1986, 974,000 kg of finfish and 620,000 kg of crabs, Callinectes spp., were caught incidentally by artisanal shrimp trawlers fishing in the Gulf of Paria. Of this total incidental catch (1,594,000 kg), about 1,500,000 kg were discarded (94 percent). Four penaeid shrimp species are targeted: Penaeus schmitti, P. notialis, P. subtilis, and Xiphopenaeus kroyeri. Callinectes spp. were caught in large quantities from Augustto mid-January. Small (4-15 cm) pelagic and demersal species of little commercial importance dominated the finfish by-catch: Harengula spp., Cetengraulis edentulus, Chloroscombrus chrysurus, Eucinostomous spp., Diapterus rhombeus, and Cyclopsetta spp. Altogether, the monthly percentage of the species ranged from 70 to 85 percent of the total finfish by-catch.

Biology and Potential Use of Pacific Grenadier, Coryphaenoides acrolepis, off California

Grenadiers (family Macrouridae) are the most abundant fish on most continental slope areas worldwide. Off California the Pacific grenadier, Coryphaenoides acrolepis, occurs in relatively large numbers and may have marketing potential. This repon provides information on the biology of the species and catch results from a number of scientific cruises. Catch data on several other species found together with Pacific grenadier, panicularly sablefish, Anoplopoma fimbria, are also given. The fish were caught with a bottom trawl (15 trawls), and with free-vehicle longline gear (117 sets). The latter was a hook and line system in which the gear was dropped to the seafloor untethered to the fishing vessel, and floated to the surface, with the catch, when detachable weights were automatically released. Sablefish dominated longline catches in depths of 200-600fm (334-1,098m), while Pacific grenadier was most abundant between 600 and 1,OOOfm (1,098-1,830m). Best trawl catches of Pacific grenadier were made at depths between 615 and 675fm (1,125 and 1,235 m) and at 760fm (1,391 m). Ripe females were absent from our samples, but spent females were found during the entire year with highest numbers in the spring and early summer. Only one larva was found despite extensive sampling with plankton nets. Pacific grenadier was found to have good edible qualities by a taste-test panel, although the protein content (15 percent) and flesh yield (24 percent) were significantly lower than those of other fishes. A second species, the giant grenadier, Albatrossia pectoralis, was found to have exceptionally poor eating qualities and even lower protein content.