Spatio-temporal trends of longline fishing effort in the Southern Ocean and implications for seabird bycatch

Longline fisheries have expanded throughout the world's oceans since major commercial distant-water pelagic fleets began fishing for tuna and tuna-like species in the early 1950s. Along with the more recent development and expansion of demersal longline fleets for species such as Patagonian toothfish, these vessels are a major source of mortality to several species of seabird. Vessels can set many thousands of baited hooks in a day across many kilometres of water. These waters are often used as foraging areas by wide-ranging seabirds. Attracted by baits and offal, the birds can be caught on the baited hooks and subsequently drown. To provide a greater understanding of the potential impact of the Southern Ocean's longline fleets on seabird populations, this paper describes the trends in longline effort of the major pelagic and demersal fisheries in southern waters. The total reported effort from all longline fleets south of 30°S has been well over 250 million hooks per year since the early 1990s. However the spatial and temporal distribution of this effort has not been constant. While effort from the Japanese pelagic distant-water longline fleet declined through the 1990s, the Taiwanese fleet expanded dramatically. Likewise demersal fishing for toothfish increased markedly during the mid-1990s. These fisheries, along with substantial illegal longline fisheries, may be placing the long-term viability of many Southern Ocean species of seabird in jeopardy.     

Understanding and addressing seabird bycatch in Alaska demersal longline fisheries

The incidental catch of seabirds in longline fisheries is a global conservation concern. In Alaska, annual seabird bycatch in demersal longline fisheries ranged between 10,300 and 26,300 birds (1995–2001). We explore the relationship between four categories of potential forcing factors (temporal, spatial, environmental, and fisheries-related) and seabird bycatch rates in Alaska demersal longline fisheries to provide practical management alternatives that could significantly reduce seabird bycatch.Separate generalized linear or additive models (GLM or GAM, respectively) were created for several combinations of seabird group, fishery and large geographic region. Across nearly all models, “vessel” was the most influential factor explaining seabird bycatch rate variation. Rather than a single variable, vessel is an amalgam of unmeasured forcing factors many of which could not be separated out in this data set (e.g., longline sink rate, vessel setting speed, line deployment location relative to propeller direction). A separate vessel-specific analysis also supported the multivariate results that performance of an individual vessel is overwhelmingly important (i.e., some vessels have consistently high or low bycatch rates from year to year). Therefore, vessel-specific performance is a critical management option.The effects of temporal (annual, month, and breeding phenology) and spatial variables were also moderately influential on seabird bycatch rates. Our results suggest that seasonal adjustments in the Alaska longline fishery have potential for overall bycatch reductions, but vague seabird management objectives could have huge unintended and undesirable consequences when implementing temporal adjustments. Other variables (environmental and other fishing-related factors) were frequently significant but contributed a small amount to overall explained deviance.Based on this study, we conclude that a vessel-specific management approach would be the most effective and efficient means to reduce seabird bycatch in Alaska.     

Integrated weight longlines with paired streamer lines - Best practice to prevent seabird bycatch in demersal longline fisheries

To evaluate a new technology - integrated weight longlines (IW) - as a viable seabird mitigation technology for demersal longline fisheries, we compared three experimental mitigation treatments, IW line alone, IW with paired streamer lines (IWPS) and unweighted longlines (UW) with PS (UWPS), to a control of no deterrent (UW alone). Trials took place on two vessels targeting Pacific cod (Gadus macrocephalus) over a five-month period in the Bering Sea, Alaska, USA. We used multiple criteria for evaluations - catch rates of all taxa, seabird abundance and attack rate, and gear sink rate and performance - making this study the largest and most comprehensive experiment of its kind.All mitigation technologies dramatically decreased seabird bycatch rates while having little to no effect on fish catch rates. Mitigation was more effective for surface foraging seabirds (Fulmarus glacialis and Larus spp.) than for diving seabirds (short-tailed shearwaters, Puffinus tenuirostris), reducing mortality rates by 91-100% and 80-97%, respectively. Based on multiple criteria, IWPS performed best, sinking gear within the protection of streamer lines eliminating surface forager catch completely and reducing shearwater catch by 97%, relative to the control. UWPS, status quo in the Alaska fishery, and IW alone performed similarly reducing surface forager catch rates by 98% and 91%, respectively, and shearwater rates by 87% and 80%, respectively. Seabird abundance and attack rate were poor proxies of seabird mortality, especially for IW gear. IW lines reduced the distance astern that birds have access to sinking baits by near half and its handling qualities proved superior to UW. We conclude that IW longlines and paired streamer lines are the core mitigation techniques and when deployed together, constitute the best management practice for seabird conservation in demersal longline fisheries using autoline systems.     

Fast sinking (integrated weight) longlines reduce mortality of white-chinned petrels (Procellaria aequinoctialis) and sooty shearwaters (Puffinus griseus) in demersal longline fisheries

Longline fisheries have been responsible for the deaths of large numbers of seabirds worldwide. Two of the most difficult seabird species to deter from baited hooks are the white-chinned petrel (Procellaria aequinoctialis) and sooty shearwater (Puffinus griseus). Longlines with integrated weight (IW) sink faster than normal, unweighted (UW), longlines and have the potential to reduce the numbers of these species killed. The relative differences in the number of white-chinned petrels and sooty shearwaters killed on UW longlines and IW longlines containing 50 g/m beaded lead core were investigated in 2002 and 2003 in the New Zealand ling (Genypterus blacodes) autoline fishery. Effects on catch rates of target and non-target fish species, and operational aspects of the use of IW gear, were also assessed. A single bird scaring streamer line was deployed on all sets of longlines. In 2002 and 2003, compared to UW lines IW lines reduced mortality of white-chinned petrels by 98.7% and 93.5%, respectively. In 2003 IW lines reduced sooty shearwater mortality by 60.5%. Catch rates of white-chinned petrels (including on sets when no fatalities were recorded) by IW gear were low: 0.005/1000 hooks (UW: 0.4) and 0.01/1000 hooks (UW: 0.17) in 2002 and 2003, respectively. Equivalent rates for sooty shearwaters in 2003 were 0.06/1000 hooks by IW and 0.13/1000 hooks by UW. No albatrosses were caught on either line type in 2002; in 2003 a single Salvin’s albatross (Thalassarche salvini) was caught on UW gear. Both the number of ling and the mean masses of ling caught in 2003 by IW (mass: 189.3; CL_95% 162.7-220.3 kg/1000 hooks) and UW (200.6; CL_95% 178.2-225.9 kg/1000 hooks) longlines were similar statistically. Use of IW longlines and streamer lines in autoline fisheries should yield major conservation benefits to seabirds interacting with these fisheries worldwide.     

Estimating the odds of survival and identifying mitigation opportunities for common bycatch in pelagic longline fisheries

To evaluate how fishing practices affect bycatch survival and to identify opportunities to reduce bycatch mortality, we estimated the odds of hooking survival for common bycatch species in the Canadian longline fishery for swordfish (Xiphias gladius) and tunas (Thunnus spp.) fishing in the North Atlantic. Generalized linear models, with binomial response, were based on 859 sets observed between 2001 and 2004 and were tested using data from 2005 and 2006. Bycatch included targeted species in poor condition or below regulatory size limits. Odds of survival were two to five times higher for swordfish, yellowfin tuna (Thunnus albacares), pelagic stingray (Pteroplatytrygon violacea), porbeagle (Lamna nasus) and blue shark (Prionace glauca) caught on circle hooks compared to J-hooks during the 2001–2004 period. Further, odds of severe hooking injuries decreased for three shark species caught on circle hooks. We found no conservation benefit for loggerhead turtles (Caretta caretta) from circle hook use. Increased circle hook use coincided with increased targeting and higher landings of tunas. Hooking survival rates and, therefore opportunities to reduce bycatch mortalities differed among the 10 species commonly discarded or released. Where the odds of survival to the time of release are high (e.g., loggerhead turtles, pelagic stingray, blue shark), methods to reduce post-release mortality can be considered. Where the odds of hooking survival are low (e.g., swordfish and longnose lancetfish, Alepisaurus ferox), methods to reduce encounter rates would have greater conservation impact.     

Artisanal longline fisheries in Southern Chile: Lessons to be learned to avoid incidental seabird mortality

Industrial longline fisheries are considered worldwide as the main threat to albatross and petrel populations, particularly at open oceans. However, inside countries’ EEZ artisanal fleets account for a significant fishing effort and eventually, could represent a major threat to these species than industrial fishing. Here we provide the first assessment of incidental mortality in two artisanal fleets in southern Chile, targeting Austral hake and Patagonian toothfish, which accounts for 0.9 and 20 millions hooks/year, respectively. Fishing techniques of these fleets have many particularities that made their operation markedly different from the more known industrial longliners, therefore their characteristics and sink rates are thoroughly described. By-catch rates (BPUE) estimated were low: 0.030 and 0.047 birds per 1000 hooks in hake and toothfish fisheries, respectively, despite that no mitigation measured was in use. These low results may reflect the fast sink rate profile of the particular longline type used by these fisheries, although the low abundance of species present may influence too. Both fleets use a modified longline having secondary hook-lines placed vertical along the mother line, each having a weight that increases significantly its sink rate, reaching 0.33 and 0.69-0.22 m s⁻¹ in the hake and toothfish longlines, respectively. Considering the big fishing effort deployed by the artisanal toothfish fleet, recommendations on mitigation measures are given for each fishery to further improve their fishing techniques.     

Seabird mortality at trawler warp cables and a proposed mitigation measure: A case of study in Golfo San Jorge, Patagonia, Argentina

We studied the interaction between seabirds and warp cables in the high-seas Argentine hake Merluccius hubbsi trawl fishery operating in Golfo San Jorge, Argentina, and tested the efficacy of a simple mitigation measure designed to reduce mortality at warp cables. Observations were made onboard hake trawlers during the height of the fishing season, between December 2004 and April 2005. Thirteen seabird species used food made available by fishing operations. The most frequent and abundant seabirds (% occurrence, mean maximum number per haul) were the Kelp gull Larus dominicanus (98.1%, 348.5) and the Black-browed albatross Thalassarche melanophrys (96.1%, 132.2). Contacts with warp cables were recorded for six species in 81.4% of hauls, with a mean number of contacts per haul of 14.4 ± 23.8 (range = 0-127). A total of 53 individuals were killed due to interactions with nets and cables, resulting in a total cable mortality rate of 0.14 birds/haul. Considering the fishery’s fishing effort, the estimated total number of birds killed during the study was 2703 (CV = 0.8), of which 306 (CV = 0.9) were killed due to contacts with warp cables (255 Kelp gulls and 51 Black-browed albatross). The tested device consisted of a plastic cone attached to each warp cable. In hauls with mitigation device, the number of contacts was reduced by 89% and no seabirds were killed. Mean distances between seabirds and cables were significantly larger in hauls with than without mitigation device (2.6 vs 0.9 m). The proposed device could be easily applied in this and other trawl fisheries operating in Argentine waters. Increased effort should be placed in implementing mitigation measures and the monitoring of cable related mortality associated to high-seas trawlers operating in the Argentine Continental Shelf.     

Interference competition in a threatened seabird community: A paradox for a successful conservation

It is often assumed that conservation actions targeting a threatened community (e.g. habitat protection) will result in similar benefits for all species. However, complex interactions between species, such as interference competition, may result in displacement of subordinate, vulnerable species. We analysed here the spatio-temporal population dynamics of a threatened seabird community since the protection in the 1980s of several breeding sites at the Ebro Delta, western Mediterranean, Spain during 1980-2007. Competition for the most suitable patches was governed by body size, with smaller species avoiding associations with larger, dominant species. We tested whether the density increase of the larger species (yellow-legged gull Larus michahellis and Audouin’s gull Larus audouinii) at La Banya (the highest quality patch within the Delta) affected species diversity at the local level. As expected, such diversity decreased, resulting also from the colonisation of other sites by smaller species, some abandoning the former area. The conservation paradox appeared because the interference competition was dominated not only by the largest species of the community, the yellow-legged gull, which is sometimes considered a pest species, but also by the vulnerable Audouin’s gull, a flagship species which has ca. 65% of the total world population at La Banya. Nevertheless, the availability of alternative patches within the Ebro Delta ensured a high biodiversity at regional scale. Results highlight the role of turnover of competing species within a community in ecosystem function and stability, and the importance of alternative sites and dispersal abilities for the conservation of vulnerable communities.     

A review of conservation threats on Gough Island: a case study for terrestrial conservation in the Southern Oceans

Gough Island is a remote Southern Ocean Island that, despite having no permanent human population, is under substantial conservation threat as a result of human activity. A considerable proportion of the flora and fauna has been accidentally introduced, and new data are presented showing that ca. 70% of the free-living pterygote insect species are introductions. We describe how endangered seabirds that breed on the island may suffer from human fisheries activities and present new evidence showing that local temperatures have risen significantly since 1963, threatening to alter the architecture and composition of species communities. These observations are an indication that the terrestrial ecosystems of other remote islands in the Southern Oceans may be under greater conservation threat than previously thought. In light of the threats described, we discuss conservation management priorities for Gough Island. To facilitate conservation of the indigenous biota, and that of similar islands elsewhere, we suggest that a combination of proactive measures designed to maintain the integrity of island communities, and monitoring programs designed rapidly to identify new conservation threats, should be implemented conscientiously.     

Disturbance to a foraging seabird by sea-based tourism: Implications for reserve management in marine protected areas

The provision of recreational opportunities is one of the important human goals of marine protected areas. However, as levels of recreational use increase, human disturbance is likely to cause significant detrimental effects upon wildlife. Here we evaluate the best managing options to mitigate the impact of sea-based tourism on the foraging activity of an endangered population of European shags, Phalacrocorax aristotelis, in a coastal marine protected area (Cíes islands, north-western Iberia). Boat disturbance elicited a characteristic avoidance behavior that resulted in a substantial reduction in foraging activity as levels of boat use increased. Moreover, boats excluded shags from the best feeding areas, resulting in higher densities of foragers in areas of little boat traffic. We used a behavioral model to explore the effects of managing strategies aimed at reducing the impact of boats on the foraging activity of shags. Our model suggested that in low boat disturbance scenarios limiting the number of boats using the reserve would be a better management option than habitat protection (i.e. the establishment of set-aside areas free of boat traffic). On the contrary, when boat disturbance levels are high the protection of habitat is recommendable, even if spatial variation in habitat quality is unknown or poorly assessed. Our study stresses the point that management strategies to minimize disturbance to foraging seabirds may depend on the spatial overlap between sea-based recreational activities and foraging seabirds and the spatial variation in marine habitat quality for seabirds.     

Does natural acidity mediate interactions between introduced brown trout, native fish, crayfish and other invertebrates in West Coast New Zealand streams?

The presence of introduced brown trout (Salmo trutta) on the distribution of native crayfish (Paranephrops planifrons), native galaxiid fishes (Galaxias spp.) and invertebrate fauna was investigated in 18 West Coast New Zealand streams (8 with trout and 10 without trout) differing in chemical characteristics. Gut contents of trout, crayfish and eels were also examined to evaluate whether competition or predation could be linked to the patterns found. Abundances of crayfish and galaxiids were significantly lower in streams with trout, but in streams without trout, substrate size was one of the most important factors determining crayfish abundance. In contrast to crayfish, other macroinvertebrates were more abundant in trout streams than streams without trout and significantly more taxa were found in streams with trout. Macroinvertebrate abundance was related to environmental factors, such as pH, substrate, depth and total nitrogen. Gut content analysis showed an overlap in diet (mostly invertebrates) between trout and eels. Crayfish, however, had a more omnivorous diet where detritus was the most frequently occurring food material. Differences in chemical characteristics marked the streams with and without trout. Thus, trout were not present in streams with pH < 6.0. Crayfish and galaxiids were present in streams with pH ranging from 4.1 to 7.9, and those with pH < 6.0 may function as trout-free refuges where larger populations of these species may persist. However, other macroinvertebrate taxa may be more negatively affected by acidification than by trout. By protecting naturally acidic, brown water streams, New Zealand crayfish and galaxiid fish populations can be conserved within geographic areas where trout are present.     

Long-term trends in lobster populations in a partially protected vs. no-take Marine Park

Increasing the level of protection afforded to the marine environment requires assessment of the efficacy of existing marine protected areas (MPAs) in protecting exploited species. Long-term data from before and after the establishment of MPAs provide a rare but valuable opportunity to assess these effects. In this study we present long-term data (1977-2005) from before and after park establishment, on the abundance of spiny lobster Jasus edwardsii from fixed sites in a no-take marine park and a recreationally fished marine park, to assess the efficacy of no-take vs. partial protection. Lobster densities were comparable between both marine parks prior to park establishment, but the response of lobster populations differed markedly following protection. On average, legal-sized lobster were eleven times more abundant and biomass 25 times higher in the no-take marine park following park establishment, while in the partially protected marine park there has been no significant change in lobster numbers. Furthermore, no difference was found in densities of legal-sized lobster between the partially protected marine park and nearby fully-fished sites (<1 per 500 m²). Long-term data from fully fished and partially protected sites suggest long-term declines in lobster populations and reflect regional patterns in catch per unit effort estimates for the fishery. The long-term patterns presented provide an unequivocal example of the recovery of lobster populations in no-take MPAs, but clearly demonstrate that allowing recreational fishing in MPAs has little benefit to populations of exploited species such as J. edwardsii.     

Expectations for population growth at new breeding locations for the vulnerable New Zealand sea lion (Phocarctos hookeri) using a simulation model

Management plans for threatened or recovering large vertebrate species that are increasing in population size and range focus on the establishment of viable populations within set temporal limits. New Zealand (Hookers) sea lions (Phocarctos hookeri) were declared a threatened species in 1997, and New Zealand legislation requires that threatened species of marine mammals must be managed to reduce human-induced mortality and achieve a non-threatened status within 20 years. The present breeding distribution of P. hookeri is highly localised, with over 95% of total annual pup production located at Auckland Islands and almost all of the remainder at Campbell Island. Breeding elsewhere has been ephemeral or restricted to <10 adult females. The only recorded sustainable breeding at a new location has been at Otago, South Island, New Zealand. This breeding population consisted of a total of four breeding females in 2002 and is derived from one immigrant female that gave birth to her first pup in the 1993/1994 breeding season. The New Zealand Department of Conservation management plan specifies that to achieve a non-threatened status P. hookeri (1) at Otago must increase in the number of breeding females to ?10, and (2) must establish ?two new breeding locations within the 20-year time frame, each with ?10 breeding females. This study 1) projects the population growth trends at a new location (Otago) to see if it will achieve ?10 breeding females within the legislated time frame, and (2) examines the likelihood that other breeding locations will establish elsewhere given the demographic information available for this species. We present 20 deterministic and three stochastic Leslie matrix model scenarios for female population growth for the initial years following the start of breeding at a new location. Our results indicate that (1) a new breeding population derived from one immigrant female is unlikely to reach 10 breeding females in 20 years; this duration is more likely to be 23-41 years (deterministic models) or 23-26 years (stochastic model), (2) the likelihood of two new sites establishing within 20 years is unquantifiable, but the probability is low, and (3) if the legislated outcome and time limit are not revised in the population management plan, the feasibility and effectiveness of re-locating young females could be investigated.     

Detection of soil moisture and vegetation water abstraction in a Mediterranean natural area using electrical resistivity tomography

Vegetation growth in semiarid, Mediterranean ecosystems is greatly dependent on moisture availability in the soil, as little precipitation is available during the growing season. Predicting the effects of climate change on vegetation development requires understanding of the exact relation between climate, moisture availability, and plant growth. Accurate moisture measurements in naturally vegetated areas are difficult because of high spatial variability and because of the coarse, shallow soils. In this study, we evaluated the possibilities of using Electrical Resistivity Tomography (ERT) to measure soil moisture availability and plant water use in a Mediterranean natural area. We found that ERT is a useful tool for measuring soil conditions, providing information on the spatial patterns within the soil and reaching depths otherwise inaccessible. In heterogeneous soils, we differentiated between lithological and moisture effects in the measurements using multitemporal data. Absolute calibration to moisture content was sometimes possible, but strongly location dependent. Based on the ERT measurements, we found that although the soils in the study area are shallow and rocky, plant roots penetrate deeply into the fractured and weathered bedrock, and vegetation subtracts water from depths down to 6 m and below. This information is important for understanding the plant–soil relations and modeling vegetation development. We conclude that ERT provides crucial information on soil moisture processes unavailable using any other currently available measurement method.