Incorporating uncertainty into the estimation of biological reference points for a spiny lobster (Panulirus penicillatus) fishery

The status of a fishery is often defined as the probability of fishing mortality rate exceeding a perilous level for long‐term sustainability. Lobster stock assessments are often subject to large uncertainty in input data and high levels of natural variability in lobster life history processes, which calls for incorporating uncertainty associated with both indicator and management reference points in an evaluation of biological risk of overfishing. Using a Monte Carlo simulation approach, we evaluated the impacts of uncertainty in modelling on the determination of the status of the Taitung spiny lobster (Panulirus penicillatus) fishery (Taiwan), which has not been quantitatively determined despite its commercial importance. The commonly used biological reference points derived from the per recruit model (F _0.1 the fishing mortality rate where the slope of the curve of yield‐per‐recruit model is 10% of the maximum slope and F _4Q%, the fishing mortality rate that reduces the expected egg production for a cohort of female lobsters to 40% of that produced in the absence of a fishery of the egg‐per‐recruit model) were influenced by uncertainties associated with lobster life history and fishery parameters. A large uncertainty in the current fishing mortality rate (F _cnr) and estimates of biological reference points (F _BRPs) increased the uncertainty in determining the risk of overexploitation throughout the confidence levels of the stochastic decision‐making framework. This simulation study suggests that the target reference point of F _40% is less sensitive to the input parameters’ uncertainty than F _0.1 We suggest a further evaluation of other F‐based references points and development of biomass‐based reference points before final selection and implementation for the management of the Taitung lobster fishery.     

Evaluating local population dynamics of the American lobster,Homarus americanus,with trap‐based mark‐recapture methods and seabed mapping

Seabed mapping, spatially referenced trapping, and mark‐recapture methods have all been useful tools in ecological studies of lobsters and other benthic animals. Here we integrate the three methods to evaluate local population dynamics and movements of American lobsters, Homarus americanus, in coastal fishing grounds in Maine, United States. The study was conducted on five study areas of different size, and used two different sampling protocols. At one site (1 km² in area) we used a monthly mark‐recapture sampling interval over a 6‐month period, only tagging a subsample of the catch. At four smaller sites (0.3 km²) we used a shorter‐term approach, sampling at 3–4‐day intervals for a 2‐week duration, tagging the entire catch. Tagging data were analysed with a modified Jolly‐Seber model adapted for continuous sampling to estimate population abundance, gains (immigration), and losses (emigration and mortality). Side‐scan sonar surveys of the seabed combined with diver‐based population surveys, stratified by substrate type, provided an independent comparison to mark‐recapture‐based estimates of abundance over the same areas. Spatial referencing of trap catch also allowed us to relate catch rates and lobster movements directly to seabed features. The longer‐term tagging data on the larger study area provided abundance estimates that were more consistent with the diver observations, and estimates of gains and losses statistically more robust, than those derived from the shorter‐term effort on the smaller sites. The flux of lobsters followed the well known seasonal movements on these fishing grounds, with gains and losses from the larger study area ranging over 1000 individuals per day, and an estimated mid‐summer peak density of >65 000 lobsters per km² (individuals >50 mm carapace length). This approach may lend itself to broader application with the American lobster.     

Movement patterns of individual migrating western rock lobster,Panulirus cygnus,in Western Australia

Abstract

Migrating and pre‐migrating western rock lobster Panulirus cygnus were tagged with datastorage tags that recorded temperature and pressure, which was converted to depth (Pressure (kPa) — surface pressure (kPa)/10)) at Dongara and Jurien Bay in Western Australia between December 2005 and December 2007. All lobsters were fitted with tag flotation devices, and returns were made by either commercial fishers or beachcombers who located detached tags. A total of 135 lobsters were released with “backpack” flotation tags, but only 84 (62.2%) of the backpacks carried data‐storage tags. Depths of release ranged from 5 to 113 m. Of the tagged lobsters released, commercial fishers recaptured 52 (38.5%), whereas 11 tags (8.1%) were found by beachcombers. At least 33%, and possibly up to 63%, of animals identified by their pale coloration as pre‐migrating individuals, failed to migrate. Those that did migrate (n = 11) were at liberty from 1 to 94 days and showed generally similar movement patterns in that they migrated only at night from darkness (after 2000 h) until after moonrise. However, their movement patterns were less constrained by the rising of the moon in deep water. Only 27% migrated nightly, compared with 73% that skipped migrating on one or more nights, to restart some days later. This latter proportion would likely have been considerably greater, but some migrating animals were only at large for short periods before recapture, and therefore had little time to show any variation to the nocturnal migration pattern. Individual speeds of migration during periods of activity were estimated for nine lobsters as 0.20 to 0.68 km h^?1, with a mean speed of 0.44 km h^?1, or 7.4 m min^?1. Improved knowledge of daily movement patterns resulting from this study provides a potentially important input into technological improvements in bait and pot design.     

Marine protected areas in Australia: Towards a coordinated rock lobster industry position

Plans by government to accelerate the establishment of a national representative system of marine protected areas (NRSMPAs) in Australia have caused increasing disquiet within the fishing industry. Rock lobster fishers have raised concerns regarding plans to establish large “multiple‐use” MPAs that may or may not contain a substantial no‐take component in the continental shelf waters adjacent to the coast. Key industry concerns including the potential impacts on present and future harvest rates are examined. The industry response to government MPA policy in each of the major jurisdictions is outlined. An industry position developed at the National Rock Lobster Congress in Perth, Western Australia (September 2003) is put forward. The position advocates the need for an adjustment scheme to account for displaced effort, the need for government commitment to the development of management plans that include the long‐term monitoring of all MPAs, and the need for a thorough risk assessment process to be conducted before the establishment of an MPA. The issues raised in this paper should be relevant to the establishment of MPAs in an international context.     

Distribution of mid‐ and late‐stage Jasus edwardsii phyllosomas: Implications for larval recruitment processes

The relative distributions of mid‐ and late‐stage phyllosomas, and pueruli, of Jasus edwardsii from five research cruises off the east coast of the North Island of New Zealand were analysed. A statistical approach was taken, using a bootstrapping with replacement method to test whether the observed mid‐ and late‐stage phyllosomas could have come from the same distribution. Differences in distribution between mid‐ and late‐stage phyllosomas were very close to significant at 95% confidence for two cruises, significant at 85% confidence for one cruise, and two cruises showed a non‐significant result. When all cruise data were combined into one analysis, the differences between mid‐ and late‐stage phyllosomas were significant with 85% confidence. On average, late‐stage phyllosomas were found 49 km further inshore than mid‐stage phyllosomas. One station during one cruise and one transect during another showed such high abundances that they affected the analyses. When these outlier data were excluded, the differences in mid‐and late‐stage distributions become significant with 99% confidence. One explanation for observed distribution differences is that the late‐stage phyllosomas swim shoreward—as the pueruli are believed to do. This implies an ability to navigate in both these early life forms. If the late‐stage larvae are indeed swimming horizontally, it is likely that this is most effectively accomplished by final‐stage phyllosomas, which have well developed pleopods, similar to those in the puerulus stage.     

THE SPINY-LOBSTER FISHERY IN CUBA*

ABSTRACT. The spiny-lobster fishery, the most valuable fishery in Cuba, is unique among those in major lobster-producing countries because of its combination of strong central control and absence of standardization and mechanization in fishing gear. Cooperation rather than competition among fishing vessels is promoted by exclusive fishing zones and fleet organization. These measures, along with the use of storage centers, simple vessels, and inexpensively constructed fishing gear, have promoted spatial rationality and cost reduction in the fishery and made it one of the most successful spiny-lobster fisheries in the world.     

Distribution of Scyllarid Phyllosoma Larvae (Crustacea: Decapoda: Scyllaridae) in the Kuroshio Subgyre

Using ichthyoplankton samples collected in the Kuroshio Subgyre during early summer cruises, we examined spatial distributions of scyllarid phyllosoma larvae in the Subgyre, particularly of the genus Scyllarus. The present study has two objectives: (1) to reveal species composition of Scyllarus phyllosoma larvae in the Kuroshio Subgyre, and (2) to examine larval recruitment of Scyllarus species as contrasted with that of Panulirus, particularly P. japonicus, the larval recruitment of which has been examined in detail. A total of 218 phyllosoma larvae collected in the present study belonged to two families (Palinuridae and Scyllaridae) representing 5 genera and 11 species. Phyllosoma larvae of two Scyllarus species (S. cultrifer and Scyllarus sp. c) were abundant among the collected larvae, and were found mainly in the following three regions located within the Kuroshio-Counter Current region south of Kuroshio Current: the water east of Okinawa Is., the water far east of Okinawa Is. (or far south of Shikoku Is.), and the water around Hachijojima Is. Larvae of each of the above two Scyllarus species collected in the three regions may belong to different populations: larvae collected in the water around Hachijojima Is. may come from their benthic populations along the Pacific coast of Honshu and Shikoku Is., central Japan, while larvae collected in the other two regions may come from their benthic populations of the Ryukyu Archipelago and Taiwan. Judging from their shorter larval period and current systems within the Kuroshio Subgyre, these Scyllarus larvae may be destined for death. An erratum to this article is available at .