Per-recruit stock assessment of wahoo (Acanthocybium solandri) in the southwest Pacific Ocean

A stock assessment incorporating sensitivity in biological parameters and potential fishery management strategies for wahoo (Acanthocybium solandri) in the southwest Pacific Ocean was undertaken to assess the stock status of this species for 2008–2010. Selectivity probabilities at age were similar for 2 commercial longline fisheries and a recreational sport fishery. However, the median exploited length and age were slightly higher in the commercial fisheries than in the recreational fishery. Current fishing mortality (Fcurrent) was predicted to be lower than limit and target reference points, with the exception that Fcurrent exceeded the target reference point FSSB40 (fishing mortality at which the spawning stock biomass per recruit [SSB/R] is 40% of the SSB/R at F=0). This result indicates that wahoo may be at a greater risk of recruitment overfishing than of growth overfishing. Of the fishery management scenarios tested, introduction of a slot limit in the recreational fishery had the greatest effect on assessment results; however, this effect was relatively minor and may not be practical to implement. Given the relatively short life span of wahoo, ongoing biological monitoring and rigorous collection of catch and effort data may facilitate continued assessment of this species in the southwest Pacific Ocean

Time-location sampling with capture-recapture to assess specialised recreational fisheries

Specialisation in recreational fisheries has led to increasing diversification and segmentation of fishers into small 'hard-to-reach' populations that are inherently difficult and costly to sample using traditional methods. In this paper, we quantitatively assess, and expand upon, time-location sampling (TLS) for a specialised recreational sport fishery off eastern Australia using stratified random sampling of fishing tackle stores as aggregation points for fishers. Multiple TLS survey events facilitated the use of capture-recapture models to provide a minimum population size estimate of 3185 (SE 1338) fishers in the study region in 2010. Adopting a questionnaire with a long recall period (e.g. 12 months) may introduce biases in estimates of effort and catch from TLS. Therefore, these biases were corrected for using a 'benchmark' on-site survey, providing minimum estimates of effort and catch of 172,438 (SE 8440) angler hours and 4.7-31.4 (SE 2.6-6.8). t for six pelagic species, respectively, in the study region during 2010. TLS with capture-recapture is an efficient method for sampling hard-to-reach specialised fishers and may yield annual estimates of population size, effort and catch. Further research is needed to refine methods and develop systematic protocols that may be applied to a wide range of hard-to-reach populations, including recreational, artisanal and illegal fisheries

Catch and effort from a specialised recreational pelagic sport fishery off eastern Australia

Recreational fisheries are undergoing increasing participation, specialisation and fishing power and contribute significantly to the total catch of several species. The specialised recreational pelagic sport fishery off eastern Australia was studied using a 12-month daytime access point survey. Sport fishing comprised 15% of the fishing trips of the 7243 recreational fishers intercepted, with the majority of fishers being male (90%) and not members of a fishing club (89%). Fishing effort, catch rates and total estimated catch varied temporally, spatially and between fishing club and non-fishing club members. A total of 25 pelagic species were retained or released by fishers and catch rates were very low (0.001-0.047 fish h(-1)). A generalised additive model incorporating environmental variables provided a useful alternative to traditional direct estimation methods for estimating total annual catch. Estimated sport fishing effort (+/-S.E.) was 63,802 (+/-5114) angler hours in 2010. Estimated total catch (+/-S.E.) for yellowtail kingfish. Spanish mackerel and wahoo ranged between 4.61 (+/-1.39) and 11.61 (+/-4.00) t and was equivalent to 27-206% of the 2010 commercial catch for these species. These results demonstrate that the catch from small specialised recreational fisheries can be significant and need to be considered in stock and resource allocation assessments. (C) 2012 Elsevier B.V. All rights reserved

Fluidity, adaptivity, and self-organization

Several recent offsite recreational fishing surveys have used public landline telephone directories as a sampling frame. Sampling biases inherent in this method are recognised, but are assumed to be corrected through demographic data expansion. However, the rising prevalence of mobile-only households has potentially increased these biases by skewing raw samples towards households that maintain relatively high levels of coverage in telephone directories. For biases to be corrected through demographic expansion, both the fishing participation rate and fishing activity must be similar among listed and unlisted fishers within each demographic group. In this study, we tested for a difference in the fishing activity of listed and unlisted fishers within demographic groups by comparing their avidity (number of fishing trips per year), as well as the platform used (boat or shore) and species targeted on their most recent fishing trip. 3062 recreational fishers were interviewed at 34 tackle stores across 12 residential regions of Queensland, Australia. For each fisher, data collected included their fishing avidity, the platform used and species targeted on their most recent trip, their gender, age, residential region, and whether their household had a listed telephone number. Although the most avid fishers were younger and less likely to have a listed phone number, cumulative link models revealed that avidity was not affected by an interaction of phone listing status, age group and residential region (p > 0.05). Likewise, binomial generalized linear models revealed that there was no interaction between phone listing, age group and avidity acting on platform (p > 0.05), and platform was not affected by an interaction of phone listing status, age group, and residential region (p > 0.05). Ordination of target species using Bray-Curtis dissimilarity indices found a significant but irrelevant difference (i.e. small effect size) between listed and unlisted fishers (ANOSIM R < 0.05, p < 0.05). These results suggest that, at this time, the fishing activity of listed and unlisted fishers in Queensland is similar within demographic groups. Future research seeking to validate the assumptions of recreational fishing telephone surveys should investigate fishing participation rates of listed and unlisted fishers within demographic groups

Rapid growth of wahoo (Acanthocybium solandri) in the Coral Sea, based on length-at-age estimates using annual and daily increments on sagittal otoliths

The wahoo (Acanthocybium solandri) is an economically important species incidentally caught in oceanic fisheries targeting tuna and coastal fisheries targeting mackerels. The age and growth of wahoo was examined using whole and sectioned otoliths from 395 fish (790-1770 mm LF) sampled from the Coral Sea. Growth increments were more reliably assigned on whole otoliths than sectioned otoliths. Edge analyses revealed that growth increments were deposited annually, primarily between October and February. Furthermore, analysis of presumed daily microincrements showed that similar to 90% of fish had deposited the first " annual" growth increment by the 365th day, thereby indirectly validating annual increment formation. Wahoo were aged at between 108 d and 7 years, with 76% of fish being,2-year old. The specialized von Bertalanffy growth function provided the best fit to length-at-age data, with parameter estimates (sexes combined) of L1 = 1499 mm LF, K = 1.58 year 21, and t0 = 20.17 years. The growth performance index for wahoo in the Coral Sea (w' = 4.55) was one of the highest of all pelagic fish, with their growth and maximum size most similar to dolphinfish. This study suggests that wahoo are one of the fastest growing teleosts and provides growth parameter estimates that may facilitate future stock assessments and guide fisheries management

Stock identification of wahoo (Acanthocybium solandri) in the Pacific and Indian Oceans using morphometrics and parasites

The wahoo (Acanthocybium solandri) is an increasingly important by-product species of tropical pelagic fisheries worldwide. However, specific management of the species is currently hindered by a dearth of information on basic biology and stock structure. This study examined the stock structure of wahoo using morphometric characters and parasite fauna from fish collected in three regions of the western Pacific, and one region in each of the eastern Pacific and eastern Indian Oceans. Similar morphometric measurements and parasite abundance of wahoo collected off eastern Australia suggest they may form part of a single phenotypic stock in the western Pacific Ocean. Morphometric measurements and parasite fauna were significantly different among wahoo from the western Pacific and eastern Pacific Oceans, suggesting multiple discrete phenotypic stocks despite genetic homogeneity. Assessing fish from a range of regions throughout the Pacific Ocean may help discriminate stock boundaries in this region. Future research using complementary techniques, such as otolith microchemistry and genetic microsatellites, may improve our understanding of the global stock structure of wahoo to suitably inform regional fishery management organizations

Reproductive biology of wahoo, Acanthocybium solandri, off eastern Australia

A dearth of basic biological information for wahoo, Acanthocybium solandri, currently hinders the ability of scientists and managers to assess population sustainability and appropriately manage the dramatically increasing global catch. This study examined the gonads of 382 wahoo collected off eastern Australia during 2008-2011 to quantify their reproductive biology in the region. The overall sex ratio of the sample was 3.2:1 (females:males), however this differed significantly among fishing sectors and areas. The estimated fork length at which 50 % of female wahoo reach maturity was 1,046 mm. Similar to the Atlantic Ocean, female wahoo have a protracted summer spawning season during October-February. The mean spawning frequency of female wahoo was uncertain but may be approximately 2-3 days, with evidence of fish actively spawning on consecutive days. Batch fecundity of females was positively correlated with fish size and estimates ranged between 0.65 and 5.12 million oocytes. Relative fecundity was estimated at 122.0 (+/- 9.7) oocytes per gram of ovary free body weight and did not differ with fish size or throughout the spawning season. Estimation of reproductive parameters such as size- and age-at-maturity may facilitate the construction of per-recruit stock assessments of wahoo in the region