Mitchell T. Zischke

Efficacy of novel sampling approaches for surveying specialised recreational fisheries

Advances in fishing technologies have increased the efficiency and diversification of recreational fisheries. This poses challenges for surveying specialised or ‘hard-to-reach’ recreational fishers (e.g. sport fishers) that may take the majority of the recreational catch for some species, but are too rare within the general population to be sampled cost-effectively using existing methods. We trialled two new methods—time-location sampling (TLS) and online diaries—for surveying specialised recreational longtail tuna (Thunnus tonggol) fishers. Results were compared with a concurrent traditional access point survey (APS). Online diaries were inexpensive but unsuitable for collecting representative data due to avidity, volunteerism, and differential recruitment bias. APS yielded high resolution data on catch, effort and size composition but was expensive and ineffective for sampling all components of the fishery. In contrast, TLS conducted at fishing tackle stores was cost-effective for accessing the breadth of fisher types due to the need for all fishers to purchase or to inspect fishing-related products at some point. Given the frequent absence of complete list frames for recreational fisheries, we suggest undertaking multiple TLS surveys to collect catch rate data and to simultaneously estimate population size using capture-recapture approaches in order to estimate the total recreational catch of species of interest.

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.

Feeding dynamics, consumption rates and daily ration of wahoo Acanthocybium solandri in Indo-Pacific waters

This study reports the diet composition of 363 wahoo Acanthocybium solandri captured from the Indo-Pacific. The study also provides the first estimates of consumption and daily ration for the species worldwide, which are important parameters for ecosystem models and may improve ecosystem-based fisheries management. Thirty-four prey taxa were identified from A. solandri stomachs with Scombridae having the highest relative importance. Actinopterygii comprised 96% of the total prey wet mass, of which 29% were epipelagic fishes, with 22% alone from Scombridae. There was no significant relationship between fish size and the size of prey items consumed. Feeding intensity, as measured by stomach fullness, did not significantly differ either among seasons or reproductive activity. The mean daily consumption rate was estimated as 344 g day-1 , which corresponded to a mean daily ration of 2·44% body mass day-1 . The results from this study suggest A. solandri is an opportunistic predator similar to other pelagic piscivores, worldwide.