Alexander I. Arkhipkin

World squid fisheries

Abstract Some 290 species of squids comprise the order Teuthida that belongs to the molluscan Class Cephalopoda. Of these, about 30–40 squid species have substantial commercial importance around the world. Squid fisheries make a rather small contribution to world landings from capture fisheries relative to that of fish, but the proportion has increased steadily over the last decade, with some signs of recent leveling off. The present overview describes all substantial squid fisheries around the globe. The main ecological and biological features of exploited stocks, and key aspects of fisheries management are presented for each commercial species of squid worldwide. The history and fishing methods used in squid fisheries are also described. Special attention has been paid to interactions between squid fisheries and marine ecosystems including the effects of fishing gear, the role of squid in ecosystem change induced by overfishing on groundfish, and ecosystem-based fishery management.

Environmental effects on cephalopod population dynamics: implications for management of fisheries.

Cephalopods are a relatively small class of molluscs (~800 species), but they support some large industrial scale fisheries and numerous small-scale, local, artisanal fisheries. For several decades, landings of cephalopods globally have grown against a background of total finfish landings levelling off and then declining. There is now evidence that in recent years, growth in cephalopod landings has declined. The commercially exploited cephalopod species are fast-growing, short-lived ecological opportunists. Annual variability in abundance is strongly influenced by environmental variability, but the underlying causes of the links between environment and population dynamics are poorly understood. Stock assessment models have recently been developed that incorporate environmental processes that drive variability in recruitment, distribution and migration patterns. These models can be expected to improve as more, and better, data are obtained on environmental effects and as techniques for stock identification improve. A key element of future progress will be improved understanding of trophic dynamics at all phases in the cephalopod life cycle. In the meantime, there is no routine stock assessment in many targeted fisheries or in the numerous by-catch fisheries for cephalopods. There is a particular need for a precautionary approach in these cases. Assessment in many fisheries is complicated because cephalopods are ecological opportunists and stocks appear to have benefited from the reduction of key predator by overexploitation. Because of the complexities involved, ecosystem-based fisheries management integrating social, economic and ecological considerations is desirable for cephalopod fisheries. An ecological approach to management is routine in many fisheries, but to be effective, good scientific understanding of the relationships between the environment, trophic dynamics and population dynamics is essential. Fisheries and the ecosystems they depend on can only be managed by regulating the activities of the fishing industry, and this requires understanding the dynamics of the stocks they exploit.

Global proliferation of cephalopods

Human activities have substantially changed the worlds oceans in recent decades, altering marine food webs, habitats and biogeochemical processes [1]. Cephalopods (squid, cuttlefish and octopuses) have a unique set of biological traits, including rapid growth, short lifespans and strong life-history plasticity, allowing them to adapt quickly to changing environmental conditions [2-4]. There has been growing speculation that cephalopod populations are proliferating in response to a changing environment, a perception fuelled by increasing trends in cephalopod fisheries catch [4,5]. To investigate long-term trends in cephalopod abundance, we assembled global time-series of cephalopod catch rates (catch per unit of fishing or sampling effort). We show that cephalopod populations have increased over the last six decades, a result that was remarkably consistent across a highly diverse set of cephalopod taxa. Positive trends were also evident for both fisheries-dependent and fisheries-independent time-series, suggesting that trends are not solely due to factors associated with developing fisheries. Our results suggest that large-scale, directional processes, common to a range of coastal and oceanic environments, are responsible. This study presents the first evidence that cephalopod populations have increased globally, indicating that these ecologically and commercially important invertebrates may have benefited from a changing ocean environment.

Thirty years' progress in age determination of squid using statoliths

The discovery thirty years ago of daily growth increments in squid statoliths and the development of statolith ageing techniques gave new insight into squid age, growth and metabolism. The techniques have shown that the majority of recent coleoid cephalopods live in the ‘fast lane’, growing rapidly and completing their life cycles in a year or less. Surprisingly, these useful approaches to the study of age and growth in squid have not gained much momentum. Only approximately an eighth of more than 300 squid species have had their basic age assessed and described. Two dozen species are subject to continuing arguments about which increments to consider as daily growth increments. This paper outlines major problems encountered during age determination of squid and suggests ways to improve the techniques and make them applicable to a wider spectrum of species.

Inverse patterns in abundance of Illex argentinus and Loligo gahi in Falkland waters: possible interspecific competition between squid?

Abstract Fishery statistics for two abundant commercial squid, Illex argentinus (Ommastrephidae) and Loligo gahi (Loliginidae), in Falkland Islands waters (southwest Atlantic) between 1987 and 1999 were analysed. The areas of the highest densities of the two species are usually separated, with I. argentinus most abundant to the north-west of the Islands in February–May and L. gahi to the south-east in February–May and August–October. However, in some years, I. argentinus intrude in great numbers into nursery or feeding areas of L. gahi in April and May. It could, therefore, affect, either directly (via predation) or indirectly (by competition for food), the abundance and recruitment of the second cohort of L. gahi , exploited around the Islands between April and October. Catch per unit effort (CPUE) of I. argentinus in February–March did not correlate with that of L. gahi in February–May. In contrast, the CPUE of I. argentinus in April–May was negatively correlated with that of L. gahi in April–May and August–October of the same year. Possible reasons for these inverse abundance patterns of the two squid species, and their implications for fisheries management are discussed.

Alternative usage of common feeding grounds by large predators: the case of two hakes (Merluccius hubbsi and M. australis) in the southwest Atlantic

Monthly variations in spatial and depth distributions, sex ratios, and maturity status in two species of hakes, Merluccius hubbsi and M. australis, were analysed in an area where their ranges overlap spatially on the shelf and slope around the Falkland Islands, and in international waters at 45–47° S (High Seas), using data collected by scientific observers on commercial fishing vessels. A variety of exploratory analyses were carried out on the raw data before patterns were quantified using generalised additive models. Both species use the areas studied as their feeding grounds. M. australis occur mainly on the Falkland shelf south of 51° S, whereas M. hubbsi is widely distributed throughout both the Falkland and High Seas shelf areas. Preliminary schemes of the seasonal migrations of both hakes in Falkland waters and on the High Seas are suggested and discussed. M. hubbsi and M. australis are found to be strongly segregated, both spatially and temporally, on their common feeding grounds, thus avoiding potential inter-specific competition for food resources.

The reproductive features of a mature female of the deep sea planktonic squid Galiteuthis glacialis (Cephalopoda: Cranchiidae) from the Southern Ocean

A mature female Galiteuthis glacialis (430 mm mantle length) was caught south of the Falkland Islands (53°S, 58°W) at a depth of 976-1001 m over a bottom depth of 1582-2378 m. A total of 8 spermatangia (15-19 mm in length) were found inserted into the mantle wall, which was of gelatinous consistency. Its ovary contained 3 605±42 oocytes, mostly 2.2-2.5 mm in length, and there were 21 ripe eggs (3.0-3.2 × 2.2-2.7 mm) in the oviducts. Only one resorpting oocyte (1.4 mm) was found. This is the only description of a mature female of this species, though two spent females have been previously described and three more mentioned by other authors.

Variation in the diet of the red cod with size and season around the Falkland Islands (south-west Atlantic)

Ontogenetic and seasonal variations in the diet were studied for a benthopelagic fish, the red cod Salilota australis (Pisces: Moridae) from the Falkland Islands shelf. The study revealed that small fish ( Loligo gahi , Illex argentinus and the fish Patagonotothen spp. being of secondary importance. In medium sized fish (40–60 cm TL) the importance of fish in their diet increased, but benthic gammarid amphipods remained important, although their role decreased in the percentage by weight. Large fish (>61 cm TL) fed mainly upon Patagonotothen spp. which consisted of 90% by weight. Seasonal variations were analysed only for medium-sized fish. In February–June, S. australis fed mainly on benthic amphipods and Patagonotothen spp. In July–October, the squid Loligo gahi became the most common prey. In November–January benthic crustaceans reappeared in the diet, and Patagonotothen spp. became the most important prey item followed by benthic gammarid amphipods and the isopod Seriolis sp. The niche breadth was found to be similar in the different size groups (2·03–2·66), indicating that the fish fed on one to two abundant prey items in each group. The niche breadth of medium-sized fish varied seasonally reflecting the diversity of prey items utilized throughout the year.

Distribution and growth in juveniles of the squid Berryteuthis magister (Cephalopoda, Gonatidae) in the western Bering sea

Abstract Seasonal distribution, size composition, age structure and growth of Berryteuthis magister juveniles (mantle length from 20 to 130 mm) were studied in the western Bering Sea (from 1700E to 179°W) between June and October 1994. According to the analysis of 1030 statoliths, the juveniles hatched from December to June with a peak in February and March. Growth data for different seasonally hatched groups were best fitted by an exponential function, summer-hatched juveniles demonstrated the fastest growth. B. magister attained the length at which it recruits (130 mm mantle length) at an age ranging from 140 to 200 days. Comparison of variability of both juvenile age structures and geostrophic currents in the region revealed that the Eastern Bering Slope Current (EBSC) was the main carrier of B. magister juveniles from the spawning grounds to the western Bering Sea. Seasonal variability of the EBSC determined the differences in juvenile migratory patterns. During its intense stage in May-June, the EBSC...

Aberrant structure of the statolith postnuclear zone in the squid Todarodes sagittatus (Cephalopoda: Ommastrephidae)

Aberrant statolith microstructure was observed in an immature female of the squid Todarodes sagittatus (Cephalopoda: Ommastrephidae) caught in the Moroccan shelf. The paralarval statolith, (a central part of adult statolith that developed at paralarval stage), showed the first 12 growth increments outside the nucleus was reversed to the posterior side of the adult statolith, and its main axis was turned perpendicularly to the main axis of the adult statolith. However, further statolith growth followed the common pattern, and the statolith acquired its normal shape at the level of 55–60 growth increments. Such aberrance in a direction of the paralarval statolith can be explained by its complete detachment from the macula statica princeps (MSP) during strong impact to the head of the paralarva (e.g. by a predator) and further occasional re-attachment of the statolith to the MSP again.