What Role Does Longline Fishing Play in the Population Decline of the Wandering Albatross?
Victor R. Bennett & Aviva A. Nelkin
The wandering albatross belongs to the Procellariiformes order and the Diomedeidae family. Members of the Diomedeidae family mate for life and lay a solitary egg, which both adults incubate. They have long pre-reproductive periods, breeding only once every two years, and reach sexual maturity at the age of 9 or older. These birds breed on various Antarctic islands where they invest much of their time and energy in parental care for their offspring. The incubation period of the wandering albatross is one of the longest in the animal kingdom, lasting 78 days (nearly 3 months), while brooding takes 9 months. This investment of time and energy usually results in high survivorship of young, but, due to the long maturity time, overall growth rate of the population is low. Unfortunately, these characteristics make the wandering albatross extremely sensitive to decreases in adult survivorship (Jouventin and Weimerskirch 1987; http://www.birdlife.org/datazone/species/index ; http://www.biodiversityinfo.org/sowb/casestudy.php?r=pressure&id=148 ).
The wandering albatrosses flight range is circumpolar its foraging range can reach up to 3600 km during the breeding season (Cuenot-Chaillet et. al. 1994). It is a pelagic, surface feeder whose diet consists of 80% (by mass) cephalopods and 20% fish, crustaceans and carrion. When foraging, albatrosses may consume around 2.1kg of food daily. This value rises to 2.2-2.4kg when brooding and drops to 1.3-1.6kg when fledging (Salamolard and Weimerskirch 1993). The annual food requirement of a population of 2,200-2,600 breeding pairs is 1.35 million kg of squid, 0.17 million kg of fish and 0.17 million kg of crustaceans and carrion (Adams et. al. 1986). In this sense wandering albatrosses play a vital role in the Antarctic food chain and, as such, have a substantial impact on ocean resources. These characteristics, along with its sensitivity to decreases in adult survivorship, have caused the wandering albatross population to decline dramatically since the 1970’s. This sharp decline coincides with a parallel increase in longline fishing industries.
Longlining is a fishing method whereby thousands of baited hooks, attached to a main line, are dragged behind the fishing vessel. Since these hooks are small and light they do not sink immediately and can therefore be swallowed by scavenging birds. Hooked birds are in danger of being dragged underwater, to their deaths, as the lines sink (http://www.birdlife.org/datazone/species/index.html?action=SpcHTMDetails.asp&sid=3952&m=0; http://www.biodiversityinfo.org/sowb/casestudy.php?r=pressure&id=148). Those birds that are able to free themselves from the hooks still may die as a result of injury and infection (Dalziell and De Poorter 1993). The wandering albatross is particularly at risk because its large foraging range overlaps with numerous longline-fishing territories. One such territory lies along the Patagonian shelf where the Patagonian tooth-fish industry is concentrated. These waters are a fed by the rich Falkland Current and are therefore a critical resource for Diomedea exulans, who feeds on its rich abundance of squid (Croxall and Wood 2002). The Japanese southern blue-fin tuna longline fisheries are also impacting the wandering albatross population. The territories for these fisheries are far more spread out (latitude 30 degrees S to 50 degrees S) and extend along the length of the wandering albatrosses circumpolar range (de la Mare and Kerry 1994). It was found that immature birds were at a greater risk of being caught by longline fishing vessels because these birds forage in more northerly areas, which coincide with longline fishing grounds (Cherel et. al. 1995; Barbraud et. al. 2008; Gales et. al. 1998). The effect of such losses on future population demographics are not immediately apparent, due to the fact that the Wandering Albatross takes approximately one decade to reach breeding age (Barbraud et. al. 2008.) It was also found that when vital breeding grounds were located close to longline fishing areas, adult birds were more vulnerable to longline fishing mortalities. This was due to the fact that their foraging ranges were restricted to waters close to their breeding site (waters which were occupied by longline tuna fishing vessels) by the presence of a brooding chick. As a result their populations were impacted dramatically (Brothers et. al. 1998). It is estimated that 9,600 wandering albatrosses are killed each year by these fishing industries (Brothers et. al. 1998). Birds are attempting to compensate for this sharp increase in adult mortality by “an advancement of 6.5 years in the mean age at first breeding (Jouventin and Weimerskirch 1987).” This results in a continuous slow decline in the wandering albatross population due to the fact that these inexperienced birds are less successful at raising chicks and avoiding fishing tackle (Jouventin and Weimerskirch 1987). Kerry and de la Mare (1994) conclude that this increase in adult mortality, adult injury, and reduction in the average age of the breeding population will lead to a rapid decline in chick survival to fledging and possibly placing the wandering albatross on the endangered species list.
Although an overwhelming majority of studies have supported the claim that the long line industry has had a hand in the decline of the Wandering Albatross, some studies have recently been conducted which challenge this claim. One study compiled a list of these arguments, such as the finding that the longline fishing industry has been quite variable over time, while the mean breeding success of the Wandering Albatross is high (and potentially rising) with very little variation, meaning that the any changes in Albatross numbers have not correlated with longline fishery patterns (Barbraud et. al. 2008). This paper also found that although the breeding success of the Wandering Albatross seemed to be on the rise, the breeding population itself was in decline. These two factors (declining breeding population and increasing breeding success) might suggest that density dependent factors were at work. It should be noted though, that the lack of a relationship between population trends and fishing efforts might be deceptive due to the fact that the majority of birds killed were immature, which therefore might lead to a lag in the way the demographic rates responded. The researchers go on to hypothesise that changes in Wandering Albatross population might, in fact, be due to increasing sea surface temperatures. Barbraud et. al. (2008) found that this was supported by research done by another research team, headed by P. Inchaustai in 2003, who found that warm sea surface temperature positively affected breeding success. Barbraud et. al. (2008) also noted that the research team of Furness and Greenwood, in 1993, believed that other environmental conditions might be causing the changes in breeding success, and that the Wandering Albatross might therefore be used as an indicator of environmental condition. It should be noted though, that Barbraud et. al. (2008) found there to be no direct relationship between number of breeding pairs, fishing vessels, and climatic conditions, which tends to cast a pall over this theory. Another paper has questioned the validity of previous studies which were used as the keystone for linking Wandering Albatross decline to the actions of the longline fishery industry. They claim that these previous studies results might have been skewed since observers would be more inclined to collect larger species (since they are more noticeable) such as the Wandering Albatross (Gales et. al. 1998). This paper then provides a counterargument by stating that those older studies might have been more accurate in their calculations of number of birds killed since the issue of bycatch was not as emotive as it is today, therefore the fisherman would have been less likely to secretly cut birds off the lines in order to minimise the number counted. They also suggest that the number of birds caught could be an underestimate since a certain number of birds hooked (possibly 30%) were potentially lost due to current or eaten before the lines are hauled in (Gales et. al. 1998).
Having read through this research (on both sides of the argument) we have come to believe that longline fishing cannot be ignored as a potential threat to the survival of the Wandering Albatross. Admittedly there are valid arguments which allow the possibility that the link between longline fishing and Wandering Albatross population decline is tenuous, but the potential disastrous cost of doing nothing far outweighs the inconvenience of the proposed preventative measures. In light of this, it is fortunate that the wandering albatross population has science and the conscience of many nations on its side. The Scientific Committee for the Conservation of Antarctic Marine Living Resources (SC-CAMLR) has proposed a number of methods for decreasing the longline fishing industries impact on the wandering albatross population. Most of these methods aim to work with the existing fisheries by modifying their techniques rather than prohibiting their activity. Some of these methods include the use of streamers on the ship to deter birds from alighting on nearby water, the utilisation of weights on ‘branch lines’ to quicken the sinking of hooks and making it more difficult for new fisheries to start in the South Atlantic (www.colby.edu/personal/t/thtieten/end-sio.html; Cherel et. al. 1995; Dalziell and De Poorter 1993). Additionally, when boats are operating at night, it was found that mortality drastically decreased when cabin lights were turned off and when conditions were cloudy and not moonlit (Cherel et. al. 1995). Contrary to previous hypotheses, it was found that the dumping of offal during line setting dramatically decreased the seabird mortality. A whopping 87% of seabirds caught were hooked during line settings which took place without the release of offal. This means that offal should be dumped while fishing lines are being set since birds will focus on this food instead of the hooks. This is only applicable in the case of the Patagonian Toothfish vessels since it takes only 11 minutes to set their lines, whilst for tuna fishing it takes 5-6 hours. This means that offal cannot be used as solution to seabird bycatch for the tuna longline fishing vessels, since a constant release of offal would not be practical for such a long period of time, but it still remains a very effective preventative measure on Patagonian Toothfish vessels (Cherel et. al. 1995). Some other preventative methods are more long term and far sighted in their scope. They focus on the education of fishermen concerning the impact seabird mortality has on the fragile Antarctic ecosystem, which could eventually have an impact on their own industry (Gales et. al. 1998). Additionally it is strongly believed that there is a need for more observers who specialize in this aspect of Antarctic ecology to be present in order to monitor bycatch more accurately (Gales et. al. 1998)
Although the future of the Wandering Albatross seems clouded with uncertainty, there is at the very least, a concerted effort to slow down its decline regardless of whether that decline is cause by the longline fishing industry, environmental conditions or the complex interplay between human and environmental factors. Only by bridging the gap between government, industry, and the public can we hope to stop the population decline and restore this exquisite species to its rightful breeding numbers, so that future generations can experience the joy of witnessing this regal species beyond the confines of a museum exhibition or textbook. Hopefully conservation efforts, such as the ones outlined by this paper, will strike a balance between supporting a thriving fishing industry and preserving one of the world’s most awe-inspiring birds, the Wandering Albatross. Coleridge called these birds “..the birds that made the breeze to blow,” it is hoped that these birds will always remain so.
References
Adams, M.J., Brown, C.R., Nagy, K.A., 1986. Energy expenditure of free ranging Wandering Albatrosses, Diomedea exulans. Physiological Zoology 59, 583-591.
Barbraud, C., Besson, D., Delord, K., Weimerskirch, H., 2008. Population trends in a community of large Procellariiforms of Indian Ocean: Potential effects of environment and fisheries interactions. Biological Conservation 141, 1840-1856.
BirdLife International (2008) Longline fishing effort overlaps with foraging hotspots for seabirds. Presented as part of the BirdLife State of the world's birds website. Available from: http://www.biodiversityinfo.org/sowb/casestudy.php?r=pressure&id=148. Checked: 28/03/2009
BirdLife International (2008) Species factsheet: Diomedea exulans. Downloaded from http://www.birdlife.org/datazone/species/index.html?action=SpcHTMDetails.asp&sid=3952&m=0. Checked: 28/3/2009
Brothers, N., Gales, R., Reid, T., 1998. Seabird mortality in the Japanese tuna longline fishery around Australia, 1988-1995. Biological Conservation 86, 37-56.
Cherel, Yves, Duhamel, G., Weimerskirch, H.,1996. Interactions between longline vessels and seabirds in Kerguelen waters and a method to reduce seabird mortality. Biological Conservation 75, 63-70.
Croxall, J.P., Wood, A.G., 2002. The importance of the Patagonian Shelf for top predator species breeding at South Georgia. Aquatic Conservation: Marine and Freshwater Ecosystems 12, 101-118.
Cuenot-Chaillet, F., Doncaster, P.C., Weimerskirch, H., 1994. Pelagic seabirds and the marine environment: Foraging patterns of Wandering Albatrosses in relation to prey availability and distribution. The Royal Society Proceedings: Biological Sciences 255, 91-97.
Dalziell, J., De Poorter, M., 1993. Seabird mortality in longline fisheries around South Georgia. Polar Record 29, 143-145.
de la Mare, W.K., Kerry, K.R., 1994. Population dynamics of the Wandering Albatross (Diomedea exulans) on Macquarie Island and the effects of mortality from longline fishing. Polar Biology 14, 231-241.
Jouventin, P., Weimerskirch, H., 1987. Population dynamics of the wandering albatross, Diomedea exulans, of the Crozet Islands: causes and consequences of population decline. Oikos 49, 315-322.
Salamolard, M., Weimerskirch, H., 1993. Relationship between foraging effort and energy requirement throughout the breeding season in the Wandering Albatross. Functional Ecology 7, 643-652.
Sustainable Development Case Studies (2008) Saving the Albatrosses: What are the Implications of New Conservation Measures for Long-line Fisheries? Available from: http://www.colby.edu/personal/t/thtieten/end-sio.html. Checked: 28/03/2009