...aimed reduce nontargeted catches of fish, while maintaining catches of the targeted broad squid (Photololigo etheridgei) and bottle squid (Loliolus noctiluca). Compared to conventional codends made with 41-mm diamond mesh, codends made with different posterior circumferences and larger 45-mm mesh had no significant effect on the catches of any species. The best performing configurations involved the installation of BRDs designed to separate organisms according to differences in behavior. In particular, versions of composite square-mesh panel reduced the total weight of bycatch by up to 71% and there was no significant effect on the catches of squid. The results are discussed in terms of the probable differences in behavior between fish and squid in codends. After this study, a square-mesh panel BRD was voluntarily adopted throughout the fishery.

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The incidental catch of nontarget organisms (termed "bycatch") by commercial fishing gears will remain an important issue in the management of fisheries. Article 7.6.9 of the Food and Agriculture Organization's Code of Conduct for Responsible Fisheries (FAO, 1995) notes "States should take appropriate measures to minimize waste, discards, catch by lost or abandoned gear, catch of non-target species, both fish and non-fish species, and negative impacts on associated or dependent species, in particular endangered species." Several options are available for achieving these aims (Hall, 1996), but the most common strategy involves technological improvements to fishing gears that reduce unwanted mortality due to fishing (Kennelly and Broadhurst, 2002).

Much research into gear design to reduce bycatch has been undertaken in demersal trawl fisheries and especially those targeting shrimp (for reviews see Kennelly, 1995; Broadhurst, 2000). This research reflects the seriousness of bycatch issues in these fisheries and, in particular, the incidental mortality of key species such as marine turtles and juveniles of commercially and recreationally important fish. Considerably less work has been done on bycatch in other fisheries, including those targeting cephalopods.

The global catch of squid has been estimated at 2.8 million tonnes (t) per year (FAO (1)). Squid are harvested with highly-selective jigs or less selective gill nets, seines and, more commonly, trawls (Rathjen, 1991; Morais da Cunha and Moreno, 1994; Simon et al., 1996). Large-scale use of pelagic gill or drift nets has been restricted because of concern about incidental catches (e.g., Burke et al., 1994; Piatt and Gould, 1994). Despite their widespread use, very little work has been done to modify towed gears so that they selectively harvest squid. In one of the few studies relevant to this issue, Glass et al. (1999) attached video cameras to the anterior sections of trawls targeting longfin squid (Loligo pealeii) in the Atlantic Ocean and observed that squid positioned themselves considerably higher in the trawl than fish. It was suggested that this difference in behavior could be used to separate catches.

In New South Wales (NSW) Australia, arrow squid (Nototodarus gouldi), mitre squid (Photololigo sp.) and southern calamari (Sepioteuthis australis) are important in the legally retained bycatch from fish and prawn trawlers working in oceanic waters. In addition, two species of squid are specifically targeted by up to 20 trawlers with modified, single-rigged prawn trawls in Broken Bay (Fig. 1). Broad squid (P. etheridgei) (typically 30-290 mm mantle length [ML] when harvested) represent the majority of the total catch (approximately 25-50 t per year since 1997), although the smaller bottle squid (Loliolus noctiluca) (30-90 mm ML when harvested) are also retained and sold, primarily as bait for recreational anglers. Additional details on the local biology of P. etheridgei can be found in O'Donnell (2004).

[FIGURE 1 OMITTED]

The designs of trawls used to catch these squid vary among operators, but all are restricted by lengths of the headline (<11 m) and sweeps (<5 m) and minimal and maximal mesh openings of 40-60 mm in the body and 40-45 mm in the codend. To maximize catches of the smaller bottle squid, all operators use codends of the minimal legal mesh size of 40 mm, with anterior sections of 100 meshes in circumference attached to posterior sections of at least 150 meshes in circumference (made with thick twine), which are designed to reduce lateral-mesh openings (Broadhurst and Kennelly, 1996).

The configuration of conventional codends in the Broken Bay squid-trawl fishery means that these trawls are poorly selective and therefore, in addition to the targeted squid, they also retain large quantities of bycatch. Preliminary data from a 3-year observer-based study of catches in the early 1990s (DPI (2)) indicated a bycatch-to-squid ratio of up to 4:1 (by weight). Although a subset of this bycatch includes some species that the fishermen are legally permitted to retain, most of the bycatch is small, unwanted fish, including juveniles of several commercially and recreationally important species. Concerns over the mortality of these individuals and the negative impacts on stocks led us to test the utility of modifications to fish- and prawn-trawl codends for improving selection of species in squid trawls. Such...

NOTE: All illustrations and photos have been removed from this article.



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