Commercial Fishery Catch Research Articles

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.

Climate regime shifts and community reorganization in the Gulf of Alaska: how do recent shifts compare with 1976/1977?

Abstract Climate regime shifts have recently occurred in the North Pacific (1998–1999) and the Arctic (2000), but the nature of biological reaction to these events is poorly understood. An index of local climate (1960–2005), and data from commercial fishery catches (1960–2004) and from small-mesh trawl surveys (1972–2005) are used to assess the impacts of these climate events in the Subarctic Gulf of Alaska. Non-linear regression showed that survey catch composition strongly responded to local climate at lags of 2 and 4 years, providing evidence of rapid ecological response to climate change in the system. A sequential regime shift detection method identified rapid change in local climate, and in survey and commercial catches following the well-documented regime shift to a positive state of the Pacific Decadal Oscillation (PDO) in 1976/1977. However, the analysis failed to detect the 1998/1999 regime shift in local climate, or in survey or commercial catches. This result is consistent with the view that the 1998/1999 climate regime shift did not represent a reversion to a negative PDO state. Local temperature increased and local sea level pressure decreased in the Gulf of Alaska during the years 2001–2005, consistent with anthropogenic warming and recent spatial reorganization in Arctic climate. There was no evidence of community reorganization following this climate event. Further observation will be required to evaluate the persistence of this new climate pattern, and the nature of community reaction to it.

Age and Growth of the Bull Shark,Carcharhinus leucas, from Southern Gulf of Mexico

Age and growth of bull shark, Carcharhinus leucas, was investigated in the southern Gulf of Mexico (Veracruz and Campeche, Mexico) from December 1993 through June 1997. Ninety-five specimens were obtained from commercial fishery catches, and vertebrae were examined from 20 males, 61 females and 14 individuals unidentified to sex. Vertebrae were examined using five different techniques to enhance the visibility of growth rings: i) alizarin red stain, ii) crystal violet stain, iii) X-ray, iv) silver nitrate stain, and v) without staining. Verification of temporal growth ring formation was done by the indirect method of marginal increment analysis. An isometric relationship was found between growth and length of centrum, is described by a linear equation. Age-at-maturity was 10 years (204 cm total length, TL) for females and 9-10 years (190-200 cm TL) for males. The oldest female was 28 (256.0 cm TL), and the oldest male was 23 (243.0 cm TL). The von Bertalanffy growth parameters were estimated for the species (L∞ = 256.4 cm TL, k = 0.1397 per year and to = -1.935), for males (L∞ = 248.4 cm TL, k = 0.1692 per year and to = -1.03), and for females (L∞ = 262.1 cm TL, k = 0.1235 per year and to = -2.44). Sexual differences for each particular growth curve were found, L∞ being the parameter that showed the greatest difference between males and females; females attain a larger size.

Dispersal of female southern elephant seals and their prey consumption during the austral summer: relevance to management and oceanographic zones

Summary Numerical models that predict trophic structure require both accurate information on prey consumption rates and estimates of spatial and temporal variation. In the Southern Ocean little information exists on the spatial and temporal patterns of resource use by predators, so we attempted to examine these patterns for an important Antarctic predator, the southern elephant seal. We (i) defined the area of the ocean used by the adult female component of the elephant seal population at Macquarie Island; (ii) quantified the time these seals spent in the different regions of the Southern Ocean; and (iii) estimated the biomass of fish and squid prey consumed per fortnight and per region. We used data from 42 post‐breeding females collected from 1992 to 2001. The data consisted of locations determined by geo‐location (based on light intensity) recorded using dataloggers. A randomized, incremental analysis of at‐sea locations indicated that a sample of 25 individuals was required to provide 95% coverage of the total area of ocean used. The greatest amount of time (44·6%) was spent in the region between the Antarctic Polar Front (APF) and the Subantarctic Front (SAF). Up to 20% of time was spent south of the Antarctic Circle or within Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) Statistical Subareas, indicating that seals from Macquarie Island are also important summer‐time predators in high Antarctic waters. The adult female population was estimated to consume 122·73–125·81 × 106 MJ for the post‐lactation foraging trip (31 142–31 925 tonnes of prey). Of this, 47·2–53·4% was consumed within the CCAMLR Statistical Subareas and the Australian and New Zealand exclusive economic zones (EEZ). Synthesis and applications. Our study emphasizes that (i) a large sample of individual seals (25) can estimate spatial trends in prey consumption; (ii) much of the estimated prey consumption occurs within fishery‐managed zones, therefore elephant seals should be included in models predicting trophic structure in the Southern Ocean; and (iii) recent commercial fishery catch within these zones is minimal relative to the prey consumed by elephant seals, but increases in fishing activity in these zones may result in competition for marine resources.

A last chance for Kutai National Park - local industry support for conservation : K. MacKinnon, A. Irving & M. A. Bachruddin, Oryx, 28(3), 1994, pp 191–198

Commercial fishery catches in Brunei Darussalam between 2000 and 2009 were used to examine changes in community structure of Brunei's marine ecosystem – a relatively lightly harvested system within a region chronically overexploited by fisheries. We found that Mean Trophic Level (MTL) has declined at a rate of 0.08 trophic levels (TL) per decade, suggesting a ‘fishing down the marine food web’ process in Brunei waters. In order to focus on changes in relative abundance of the more threatened, higher TL finfish only, MTL was recalculated as 3.30MTL (to exclude catches of finfish and invertebrates species with TL less than 3.30). Here, we found no overall trend in the 3.30MTL over the study period. However, a more in-depth analysis suggested that MTL fails to capture substantial changes in underlying species assemblage. Over the course of the study period, marked changes in fish community structure were observed. Analysis of official statistics showed an increase in total catch was driven primarily by an increase in pelagic catches, with a similar trend observed when the catches were aggregated into either high- or low-TL. This pattern is consistent with the increasing Fishing-in-Balance (FiB) index for the Brunei region. Whilst our study was not aimed at demonstrating overfishing as the cause of observed trends, there is a danger that current best practice fails to detect what may be an imminent fishery collapse. In many fisheries around the world, there is a need for detection methods able to identify potential problems within a time scale short enough to be able to react effectively.

Comparison of commercial fishery and research catch data

Comparison of commercial fishery and research catch data

Wind-Aided Recruitment of Canadian Arctic Cisco (Coregonus autumnalis) into Alaskan Waters

Summer wind data collected at Barter Island, Alaska, were compared with commercial fishery catches of arctic cisco (Coregonus autumnalis) at the Colville River, Alaska, for the period 1967–85. There was a significant (p = 0.036) association between yearly catch-per-unit-effort and the percent of easterly winds after adjusting for a 5-yr differential in the two time series. Results suggest that young-of-the-year fish which spawn in Canada's Mackenzie River are aided in their westward dispersal into Alaskan waters via wind-driven longshore currents. The greater the prevalence of easterly winds (westerly currents), the greater the recruitment. Increased recruitment manifests itself as an increase in Alaskan commercial fishery catch some 5-yr later when fish have grown to a size that renders them susceptible to commercial nets.

Preferred Wavelengths of Visible Light for Juvenile Atlantic Menhaden

Juvenile Atlantic menhaden (Brevoortia tyrannus) from Chesapeake Bay tributaries were tested for preferred wavelengths of visible light. Fish were subjected to test gradients from 460 to 660 nm at 20 nm intervals in a test trough, and light-and dark-acclimated fish were tested at three light intensities (0.1, 0.2, and 0.4 μEm −2 s −1). These fish exhibited a preference (P ≲ 0.05) for 460-540 nm wavelengths in all tests, and a concentration in the 460-500 nm wavelengths at the higher light intensities (0.2 and 0.4 μEm −2 s −1). Knowledge of these preferred light wavelengths can be helpful for increasing commercial fishery catches and lowering the industrial impingement rates in water intake systems.

Use of Variation in Biological Characters for the Classification of Anadromous Rainbow Smelt (Osmerus mordax) Groups

Analysis of meristics, growth patterns, and fecundity to somatic weight relationships of spawning anadromous rainbow smelt (Osmerus mordax) in Quebec waters demonstrated the existence of three geographical groups (Chaleur Bay, south shore of the St. Lawrence Estuary, and Saguenay Fjord). Although homing to spawning rivers does not appear to occur, the degree of heterogeneity of spawning smelt of different geographical areas is less at the extremes of their Quebec distribution. Classification of smelt from the commercial fishery catch indicates limited mixing of these groups during open-water migration. The existence of a fourth group is suggested by classification analysis of smelt caught along the lower north shore of the St. Lawrence Estuary.