Billfish Fishery Research Articles

Environmental determinants of the at-sea distribution of encounters between flesh-footed shearwaters Puffinus carniepes and fishing vessels

Fisheries observer data were used to model the distribution of seabird encounters in order to identify potential areas for fisheries closures. Data from the Australian Eastern Tuna and Billfish Fishery (ETBF) in the Tasman Sea were used, and the focal species was the flesh-footed shearwater Puffinus carneipes Gould, 1844 (the species most commonly killed in this fishery). Encounters between flesh-footed shearwaters and longline fishing vessels varied with season, distance from Lord Howe Island, and a number of environmental and oceanographic variables. Encounters were most common south-west of Lord Howe Island, in waters associated with the Tasman Front and the East Australian Current. The resulting model was used to predict overlaps between fisheries and flesh-footed shearwaters during 3 years (1997-98, 2003-04 and 2006-07). During 2003-04, high rates of interaction were predicted in areas with high fishing effort and high observed mortality rates of shearwaters. In 2006-07 most fishing was well to the north of areas with predictions of high interaction rates, and seabird bycatch was low. The shift in fishing locations coincided, and was likely driven by, a change in the fish species targeted by the majority of the fishery. This indicates that the most likely reason for falling bycatch rates in this fishery were movements of the fishing effort away from the birds, rather than changes in fishing technique. These results emphasise the potential of area closures as a method of bycatch mitigation for species that are proving intractable to standard bycatch reduction methods. Our results demonstrate that data collected from fisheries vessels can be used to identify characteristic areas of interactions.

Spawning aggregation of the lanternfish Diaphus danae (family Myctophidae) in the north-western Coral Sea and associations with tuna aggregations

A spawning aggregation of the lanternfish Diaphus danae in the Coral Sea, that is fed on by spawning aggregations of yellowfin and bigeye tuna, has been sampled by mid-water trawling for the first time. Males and females in the aggregation occurred at a ratio of 23 to 1 and occupied two non-overlapping size classes (males 71.2–95.1-mm standard length (SL), females 99.0–121.4-mm SL). Hydrated oocytes with single oil droplets, which indicated imminent spawning, were in higher proportion in the first trawl (2134 hours to 2234 hours) than in the final trawl (0324 hours to 0424 hours) through the aggregation. Maximum estimated female D. danae fecundity (25 803) and gonadosomatic index (34.01) were higher than for any other lanternfish species recorded. Bigeye tuna (Thunnus obesus) individuals collected from aggregations were estimated to have 81–319 D. danae specimens in their stomachs. The annual Coral Sea D. danae aggregation is the only confirmed lanternfish spawning aggregation in Australian waters. The D. danae spawning aggregation provides a rich, transient foraging resource for spawning bigeye and yellowfin tuna in the Coral Sea, these being the only known tuna spawning aggregations in the Eastern Tuna and Billfish Fishery.

Monitoring the behaviour of longline gears and the depth and time of fish capture in the Australian Eastern Tuna and Billfish Fishery

We describe the results of a detailed monitoring program undertaken to understand the fishing practices and operational characteristics of longline gears deployed in the Australian Eastern Tuna and Billfish Fishery. Gear monitors were used to ascertain both the time-at-depth-profiles of the deployed longline hooks and the time- and depth-profiles of fish capture. Operational details and environmental conditions recorded by observers were also used to gain an understanding of factors influencing the depths attained by hooks and the shape of the longline. The results indicate that while hooks fish a range of depths down to around 400m the most common depths fished are relatively shallow, with 34 percent of all hooks deployed during the project period being between 40 and 60m. The depths to which hooks were observed to sink were found to be highly variable for a given longline configuration and hook-number, though the mean depths attained across sets were found to be reasonably well predicted by the longline catenary equation. Current-speed, hook-position and wind-speed were found to be the main factors influencing variation from the predicted depth. While the depth profiles fished by sets deploying less than 10 hooks-per-float were found to be similar, for sets deploying 10 or more hooks-per-float a near linear relationship was found in the mean depth fished by all hooks and the number of hooks-per-float. Finally, a procedure is outlined to estimate the availability-by-depth of the species caught and the resulting profiles were found to be similar to profiles obtained from studies using archival tags. The results of this study support the need to improve the information used to account for factors influencing the fishing effectiveness of longline gears and the use of set-based analyses to standardise catch rates.

Local management of a “highly migratory species”: The effects of long-line closures and recreational catch-and-release for Baja California striped marlin fisheries

Management of highly migratory fish species is generally assumed to require complicated international agreements. The effects of spatial closures for such species are thought to be diluted by their extensive movements. We tested these assumptions using a case study of striped marlin ( Kajikia audax) fisheries off of Baja California, Mexico. Beginning in 1977, Mexico instituted a series of long-line fishery closures and closed areas to reduce commercial fishing mortality rates on billfishes. Using data from the Japanese long-line fishery and the recreational billfish fishery in a stock reduction analysis (SRA) model, we show that temporary closures of Mexico’s EEZ to long-lining from 1977–1980 and 1984–1985 had a rapid effect on local abundance of striped marlin. Regional striped marlin abundance likely increased by 12–22% following the 4-year closure and 6–12% following the 2-year closure. Increases near Baja California may have been larger. Recreational catch-and-release appears to have a more modest effect because catches in the recreational fishery are substantially smaller than historic long-line catches. A 100% release rate over the 10-year period for which recreational catch data were available would likely have increased regional abundance by 2.8–7.5% relative to no recreational release. There is also evidence for a small effect of the El Niño Southern Oscillation (ENSO) on recruitment or net immigration, with stronger recruitment or net immigration during the cooler La Niña phase.

Ecological effects of longline fishing and climate change on the pelagic ecosystem off eastern Australia

Pelagic longline fisheries target (or catch incidently) large apex predators in the open ocean (e.g. tunas, billfish and sharks) and have the potential to disrupt the ecosystem functionality if these predators exert strong top–down control. In contrast, warming of oceans from climate change may increase bottom–up effects from increases in primary productivity. An ecosystem model of a large pelagic ecosystem off eastern Australia was constructed to explore the potential ecological effects of climate change and longlining by Australia’s Eastern Tuna and Billfish Fishery. The model reproduced historic biomass and fishery catch trends from 1952 to 2006 for seven functional groups. Simulated changes in fishing effort and fishing mortality rate on individual target species from 2008 to 2018 resulted in only modest (<20%) changes in the biomass of target species and their direct predators or competitors. A simulated increase in phytoplankton biomass due to climate change resulted in only small increases (<11%) in the biomass of all groups. However, climate-related changes to the biomass of micronekton fish (−20%) and cephalopods (+50%) resulted in trophic cascades. Our results suggest there may be ecological redundancy among high trophic level predators since they share a diverse suite of prey and collectively only represent <1% of the total system biomass. In contrast, micronekton fishes and cephalopods have high biomasses and high production and consumption rates and are important as both prey and predators. They appear to exert ‘wasp–waist’ control of the ecosystem rather than top–down or bottom–up processes reported to drive other pelagic systems.

Cyclonic and anthropogenic influences on tern populations

Organisms can be strongly affected by a range of natural and anthropogenic stressors in conjunction, making comprehensive assessments of multiple potential drivers of population dynamics essential. An 18-year dataset obtained for Michaelmas Cay in the northern Great Barrier Reef, Australia, was used to assess population trends for three tern species relative to two potential threatening processes, namely human impacts (as either commercial fishing or tourism) and cyclone activity. We found a positive, 2-year lagged relationship between long-line catch per unit effort in the Eastern Tuna and Billfish Fishery in the vicinity of Michaelmas Cay and breeding participation in the two pelagic foraging terns, but not in the inshore foraging tern. The abundance of large pelagic fish may influence recruitment into the breeding populations of the two pelagic terns in the following years through impacts on prey availability. Long-term population trends for all seabirds were not related to localised direct disturbance from cyclones or associated changes in cay size and/or nesting habitat. Current management protocols in place for the tourism industry at the cay appear to be minimising direct human impacts. Other evidence from this breeding location suggesting that climate variation may be driving foraging success and breeding-population dynamics in the two pelagic terns implies that a precautionary approach is warranted to the management of any potential stressors to birds in this system.

Using biometrie measurements to determine gender of Flesh-footed Shearwaters, and their application as a tool in long-line by-catch management and ecological field studies

We examined sexual dimorphism in 11 morphological characters of the Flesh-footed Shearwater (Puffinus carneipes) and used these characters in a discriminant function analysis (DFA) to enable sexual classification in the field. We also used molecular techniques to determine gender in live birds. Sexual dimorphism was present in all characters tested, with males (n = 50) significantly larger than females (n = 52) in all cases. A stepwise DFA of the 11 morphological characters resulted in gender being correctly assigned in 91% of birds using head—bill length (HBL), minimum bill-depth (MBD), and superior unguicorn-width (SUW), using the generalised function–48.360 + (0.661 X SUW) + (0.931 X MBD) + (0.334 X HBL). Of the nine misclassifications, seven were a result of females being incorrectly assigned as males, indicating an overlap between the upper cut off value for females with the lower threshold value for males. We applied the DFA to an existing morphometric dataset (n = 219) of Flesh-footed Shearwaters caught as incidental by-catch from long-line fishing in the Eastern Tuna and Billfish Fishery. The generalised discriminant function derived from live birds performed poorly when applied to the by-catch sample (only 68.5% correctly sexed), and the issues of data consistency and the application of discriminant functions between populations are discussed. A two-character DFA constructed from the by-catch dataset (–30.128 + 0.206 X HBL + 0.848 X MBD) resulted in 86% of by-catch birds being correctly sexed. The findings suggest that a combination of the morphological traits HBL, MBD and SUW are sufficiently robust to use in the field to determine the gender of live birds. The merits and application of this technique are discussed in relation to seabird conservation and management.

Near real‐time spatial management based on habitat predictions for a longline bycatch species

Abstract Southern bluefin tuna (SBT), Thunnus maccoyii (Castelnau), is a quota‐managed species that makes annual winter migrations to the Tasman Sea off south‐eastern Australia. During this period it interacts with a year‐round tropical tuna longline fishery (Eastern Tuna and Billfish Fishery, ETBF). ETBF managers seek to minimise the bycatch of SBT by commercial ETBF longline fishers with limited or no SBT quota through spatial restrictions. Access to areas where SBT are believed to be present is restricted to fishers holding SBT quota. A temperature‐based SBT habitat model was developed to provide managers with an estimate of tuna distribution upon which to base their decisions about placement of management boundaries. Adult SBT temperature preferences were determined using pop‐up satellite archival tags. The near real‐time predicted location of SBT was determined by matching temperature preferences to satellite sea surface temperature data and vertical temperature data from an oceanographic model. Regular reports detailing the location of temperature‐based SBT habitat were produced during the period of the ETBF fishing season when interactions with SBT occur. The SBT habitat model included: (i) predictions based on the current vertical structure of the ocean; (ii) seasonally adjusted temperature preference data for the 60 calendar days centred on the prediction date; and (iii) development of a temperature‐based SBT habitat climatology that allowed visualisation of the expected change in the distribution of the SBT habitat zones throughout the season. At the conclusion of the fishing season an automated method for placing management boundaries was compared with the subjective approach used by managers. Applying this automated procedure to the habitat predictions enabled an investigation of the effects of setting management boundaries using old data and updating management boundaries infrequently. Direct comparison with the management boundaries allowed an evaluation of the efficiency and biases produced by this aspect of the fishery management process. Near real‐time fishery management continues to be a realistic prospect that new scientific approaches using novel tools can support and advance.

The impact of pelagic longline fishing on the flesh-footed shearwater Puffinus carneipes in Eastern Australia

The flesh-footed shearwater (Puffinus carneipes) is a medium-sized seabird (ca. 700g) that is incidentally killed during longline fishing operations. We examined the levels of bycatch in Australia’s Eastern Tuna and Billfish Fishery and developed a model to examine the impact of this fishery on the eastern Australian population of flesh-footed shearwaters, which breeds at only one site, Lord Howe Island. Observed bycatch rates for flesh-footed shearwaters were 0.378 birds/1000 hooks for night sets, and 0.945 birds/1000 hooks for day sets. The mean number of birds killed from 1998 to 2002 was estimated to be 1794–4486 birds per year, with the estimated total killed over this period ranging from 8972 to 18,490 birds. Models incorporating both density-independent and density-dependent scenarios were applied to levels of bycatch representative of that observed in the fishery. Density-independent scenarios showed that fishing mortality levels caused declines in the majority of simulated populations. In contrast, density-dependent scenarios produced populations that were more resilient to fishing mortalities. Although some modelling scenarios led to population growth, under most stochastic simulations median population halving and quasi-extinction times were less than 55 and 120 years, respectively. We conclude that the level of bycatch observed in the fishery is most likely unsustainable and threatens the survival of the Lord Howe Island population. This situation can be improved only with the development and implementation of mitigation measures that will halt or greatly reduce the level of bycatch currently observed. Improved knowledge on a range of demographic parameters for the species, combined with a clearer idea of the at-sea distribution of breeding and non-breeding shearwaters, will greatly assist in improving understanding and the management of this population.

Social and economic perspective on recreational billfish fisheries

At the Second International Billfish Symposium in Kona, it was reported that little was known about the social and economic aspects of recreational billfish fisheries. There was plenty of background, some good questions, but few answers. There had been little history of social science involvement in fisheries management at the time and even less in billfish fisheries. Whether authorized or not, fishery management decisions worldwide are going to be made on the basis of ‘best available’ social and economic understanding. Unfortunately, the values held by many in the billfish angler community are not likelyto be well represented in the mix for various reasons. Research in the USA and in Latin America over the past 13 years hasprovided an understanding of the billfish angler constituency, its commitment to catch and release and support for resource conservation, its local and regional impacts on tourism economies, and its willingness-to-pay above andbeyond trip costs (a measure of user value) in the US Atlantic, Puerto Rico, Costa Rica and Mexico Pacific. Although knowledge of the recreational billfish fishery has improved, comparatively little is known about the social and economic benefits associatedwith commercial (direct and bycatch) billfish fisheries. With little more than dockside prices available in many localities, it is difficult to know their value in comparison with recreational fisheries and the possible trade-offs associated with various management measures. In addition to describing what is still not known, this paper will identify a future research agenda in this area.

Historical review of the billfish management in the Mexican Pacific

Off the Mexican Pacific coast, high catch rates are found for striped marlin, sailfish and swordfish, and to a lesser extent for blue marlin and black marlin, making this area an important fishing ground for commercial and sport-fishing fisheries. This paper focuses on the development of the billfish fisheries and their management in the Pacific waters of Mexico. Three periods are described: (1) 1900–1959, (2) 1960–1989 and (3) 1990 to the present. During the period of 1900 to 1959, sport fishing began to develop, resulting in important tourist resorts. A system of fishing permits for this incipient fishery went into forte. Also during this period, Mexico established a territorial sea jurisdiction of 9 nautical miles. From 1960 to 1989, commercial fishing for billfish began in Mexico, with the arrival of the Japanese tuna longline fishery, where billfishes were taken as by-calch. Then, with the establishment of the 200-nautical-mile Exclusive Economic Zone (EEZ), Mexico developed its own longline fishery at the beginning of 1980. Because of the fishing interactions between the sport and commercial fisheries, efforts to manage both fisheries were undertaken. At the beginning of the third period (1990 to the present), the commercial fishing for marlin and sailfish in Mexico was prohibited and only commercial fishing for swordfish is allowed today. Recently, a plan for the development of the sport fishery was published, and regulations on bag limits and fishing gear were established. Although billfish are highly migratory species, Mexico asserted its right to manage this species unilaterally in its EEZ. The sport-fishing industry represents a high value input to its economy, but only operates within the fírst 50 nautical miles of its EEZ. The lack of patrol, enforcement and presence of commercial fishermen offshore has resulted in some illegal fishing activities by foreign fishing vessels.