M. A. Steer

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.

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.

Embryonic development of southern calamary (Sepioteuthis australis) within the constraints of an aggregated egg mass

A post-cleavage embryological scheme was established for southern calamary Sepioteuthis australis. Using this developmental scheme, intra- and interspecific comparisons were made. Sepioteuthis australis development most closely resembled that of its tropical congeneric species, S. lessoniana, with only a few subtle heterochronies. The greatest developmental difference was observed when comparisons were made with Loligo pealei. These differences were attributed to developmental duration and respective egg sizes. Within S. australis, variation in developmental rates among embryos was associated with the size of the egg mass, with less variation evident in smaller egg masses. Embryos located on the periphery of the egg mass and at the distal or unattached end of an individual egg strand developed significantly faster than those located deep within the egg mass. On average, embryos in small egg masses, consisting of five individual egg strands, developed significantly faster than those in dense aggregations (>100 strands).

Population characteristics of southern sea garfish (Hyporhamphus melanochir, Hemiramphidae) in South Australia

Population dynamics, demography and spatial distribution of an important species of ‘halfbeak’, the southern sea garfish (Hyporhamphus melanochir), were studied in South Australia, which accounts for most of the national catch. Commercial catch and effort data were used to indicate spatial and temporal abundance. Catch sampling provided fish measurements and estimates of age, sex and reproductive maturity. Catches were from throughout South Australia’s gulf region, but three areas separated by hundreds of kilometres produced the highest catches. These relatively protected areas support extensive beds of intertidal and subtidal seagrasses. Statewide commercial fishery catches demonstrated considerable inter-annual variation of 240–320 t year–1. Catches were dominated by 1+ and 2+ fish, with few individuals from the 3+ to 5+ age classes. Females dominated the sex ratios, were the largest individuals, and the largest from each age class. No running ripe fish were sampled. Seasonal variation in the catch and in the lack of spawning fish suggested that adults might move from fishing areas during the spawning season. Length/weight and length/age relationships did not differ between areas separated by hundreds of kilometres, suggesting large-scale movement. Possible population truncation related to fishery exploitation has prompted a stock rebuilding program for the South Australian stock.

Evidence for a broad-scale decline in giant Australian cuttlefish (Sepia apama) abundance from non-targeted survey data

Little is known about the population trajectory and dynamics of many marine invertebrates because of a lack of robust observational data. The giant Australian cuttlefish (Sepia apama) is IUCN-listed as Near Threatened because the largest known breeding aggregation of this species in northern Spencer Gulf, South Australia, has declined markedly since the turn of the century. We used by-catch records from long-term trawl surveys to derive abundance data for S. apama and commercial cuttlefish harvest data as a measure of exploitation. Using Bayesian hierarchical models to account for zero-inflation and spatial dependence in these abundance counts, we demonstrated a high probability of broad-scale declines in the density of S. apama, particularly surrounding the primary aggregation site, which supports the recent closure of the entire S. apama fishery in northern Spencer Gulf. Historical harvest data were positively correlated with S. apama density estimated from the trawl surveys, suggesting that the commercial cuttlefish catch tracks the species abundance. Our results also indicated the possibility that the known S. apama breeding grounds might be supplemented by individuals that were spawned elsewhere in northern Spencer Gulf.

Spatial variation in shape of otoliths for southern garfish Hyporhamphus melanochir – Contribution to stock structure

Abstract Otolith morphometrics and shape analyses were used to delineate the sub-population structure and determine the level of mixing of southern garfish in South Australian waters. Adult garfish from the 2+ age class were collected from three sites within each of six regions along the South Australian coast: Northern Gulf St Vincent, Southwest Gulf St Vincent, Kangaroo Island, Northern Spencer Gulf, Southern Spencer Gulf and the West Coast of Eyre Peninsula. This study adopted a multi-stage statistical approach exploring the spatial variation in gross otolith morphology and through elliptical Fourier analysis separately, and in combination, over both broad (regional) and fine (site) spatial scales. Stepwise discriminant function analysis revealed significant separation across both spatial scales; however, overall classification success of garfish to their site of capture was poor (<45%). Despite this, the results indicated some level of structuring within South Australias southern garfish population, as fish were correctly classified at rates that were 32% better than would be expected by chance. At least six putative regional components with various levels of intermixing were detected based on differences in otolith shape. This result refines the spatial resolution of the fishery and consequently highlights the vulnerability of these regional components to localized depletion, particularly as the resource is currently considered to be over-exploited.