Guy Duhamel

Factors affecting the number and mortality of seabirds attending trawlers and long-liners in the Kerguelen area

Abstract The factors affecting the number and the mortality rates of seabirds attending long-liners and trawlers fishing in the Kerguelen area were studied during four successive seasons (1994–1997), based on observations carried out onboard by dedicated observers. Twenty-four species of seabirds were observed attending fishing vessels, representing an average of 591 birds/census. The total numbers attending varied mainly according to the year, the cloud cover and the presence of offal from long-liners. The dumping of offal increased the numbers of birds attending the vessel, especially when the offal could be easily handled by birds. The activity of the vessels also affected the numbers attending, birds being more abundant during line setting and trawl hauling. White-chinned petrels were the most abundant ship-following seabirds, followed by black-browed albatrosses, giant petrels and cape petrels. The number of white-chinned petrels, black-browed and grey-headed albatrosses attending fishing vessels increased in the time between spring and autumn, whereas it was the reverse situation for giant petrels and cape petrels. Four species of seabirds were caught by fishing gear, mainly by long-lines: white-chinned petrels, and black-browed, grey-headed and wandering albatrosses. Taking into account the number of birds from each species attending long-liners and known to be potential by-catch, some species appear to be more susceptible to being caught than others. White-chinned and grey-headed albatrosses are caught in much higher proportions than the numbers present, whereas black-browed albatrosses are caught in lower numbers. Giant petrels are abundant around long-liners but were never caught. In long-liners, most birds were killed when the lines were set during the day or when the deployment of the scaring device was not successful, with an overall figure of 0.47 birds/1000 hooks. Only one albatross was caught when the lines were set during the night. White-chinned petrels represented 92.2% of all birds killed by long-liners. The number of birds caught varied significantly among months and among years. The type of bait used also affected the catch rate. The catch rate was related to the number of birds attending the long-liner only for black-browed albatrosses. Most birds killed by trawlers were entangled by the netsonde cable. The efficiency of mitigation measures in order to reduce seabird mortality is discussed and it is stressed that night setting is the most efficient way to reduce mortality and should be enforced everywhere when possible. However, further methods should be developed to reduce the mortality of species active at night, especially white-chinned petrels whose populations in the Indian Ocean may by threatened by long-line fisheries.

Interactions between longline vessels and seabirds in Kerguelen waters and a method to reduce seabird mortality

Abstract A longline fishery for Dissostichus eleginoides has recently developed in the vicinity of South Georgia and Kerguelen islands, two internationally important breeding areas for procellariiform birds. The number of hooked birds and a method to reduce mortality were investigated during 13 days of fishing activity in Kerguelen waters in February 1994. Between 100 and 600 seabirds were always observed behind the longline vessel during daytime. The main ship-following species were the white-chinned petrel Procellaria aequinoctialis (67% of counts), giant petrels Macronectes spp. (8%) and the wandering albatross Diomedea exulans (11%), black-browed albatross D. melanophris (6%) and grey-headed albatross D. chrysostoma (2%). Only diving species were caught on the lines, i.e. the white-chinned petrel (n = 36) and the grey-headed albatross (n = 2). Marked differences in the mortality rate were observed between day and night (1·00 versus 0·38 birds per 1000 hooks), and at night when the decklights were on or off (0·59 versus 0·15 birds per 1000 hooks). Dumping of homogenized offal during line settings greatly reduced incidental capture of seabirds, mainly because birds were more attracted by offal than by hooked baits. We therefore propose that the dumping of offal during line settings should be included in the regulations of the longline fishery for Dissostichus in order to minimize seabird mortality.

Is the Species Flock Concept Operational? The Antarctic Shelf Case

There has been a significant body of literature on species flock definition but not so much about practical means to appraise them. We here apply the five criteria of Eastman and McCune for detecting species flocks in four taxonomic components of the benthic fauna of the Antarctic shelf: teleost fishes, crinoids (feather stars), echinoids (sea urchins) and crustacean arthropods. Practical limitations led us to prioritize the three historical criteria (endemicity, monophyly, species richness) over the two ecological ones (ecological diversity and habitat dominance). We propose a new protocol which includes an iterative fine-tuning of the monophyly and endemicity criteria in order to discover unsuspected flocks. As a result nine « full » species flocks (fulfilling the five criteria) are briefly described. Eight other flocks fit the three historical criteria but need to be further investigated from the ecological point of view (here called « core flocks »). The approach also shows that some candidate taxonomic components are no species flocks at all. The present study contradicts the paradigm that marine species flocks are rare. The hypothesis according to which the Antarctic shelf acts as a species flocks generator is supported, and the approach indicates paths for further ecological studies and may serve as a starting point to investigate the processes leading to flock-like patterning of biodiversity.

Interpopulation relationships in two species of Antarctic fish Notothenia rossii and Champsocephalus gunnari from the Kerguelen Islands: an allozyme study

Enzymatic polymorphism was used to detect variability within Notothenia rossii from two sites on the Kerguelen Plateau and Champsocephalus gunnari from the same sites and the South Orkney Islands. No polymorphism was found in the second species and it was low but not statistically significant in the first. This apparent homogeneity does not substantiate suggestions from other results that the populations can be separated, especially in the case of C. gunnari . Other approaches will be necessary to solve definitively the question of population separation.

Lead–radium dating provides a framework for coordinating age estimation of Patagonian toothfish (Dissostichus eleginoides) between fishing areas

Patagonian toothfish (Dissostichus eleginoides) or ‘Chilean sea bass’ support a valuable and controversial fishery, yet their life history is not well understood and longevity estimates range from ~20 to >50 years. In this study, lead–radium dating provided valid ages for juvenile to older adult groups, which were consistent with the counting of otolith growth zones in transverse otolith sections, and longevity estimates exceeding 30 years. Lead–radium dating revealed minor biases between the radiometric age and interpretation of growth zone counting for regional fishing areas monitored by two facilities, Center for Quantitative Fisheries Ecology (CQFE) and the Central Ageing Facility (CAF), using different age estimation techniques. For CQFE, under-ageing of ~3.3 years was observed for individuals with estimated ages under 20 years. For the CAF, ages were overestimated for young fish and underestimated for the oldest fish. Lead–radium dating detected underlying problems in coordinating age estimation between geographically separated fish stocks, and provided a framework to objectively assess otolith interpretation and growth modelling between laboratories based on age-validated data.

Killer whale ( Orcinus orca ) interactions with blue-eye trevalla ( Hyperoglyphe antarctica ) longline fisheries

Over the past five decades, marine mammal interactions with fisheries have become a major human-wildlife conflict globally. The emergence of longline fishing is concomitant with the development of depredation-type interactions i.e., marine mammals feeding on fish caught on hooks. The killer whale (Orcinus orca) is one of the species most involved in depredation on longline fisheries. The issue was first reported in high latitudes but, with increasing expansion of this fishing method, other fisheries have begun to experience interactions. The present study investigated killer whale interactions with two geographically isolated blue-eye trevalla (Hyperoglyphe antarctica) fisheries operating in temperate waters off Amsterdam/St. Paul Islands (Indian Ocean) and south-eastern Australia. These two fisheries differ in the fishing technique used (vertical vs. demersal longlines), effort, catch, fleet size and fishing area size. Using 7-year (2010–16) long fishing and observation datasets, this study estimated the levels of killer whale interactions and examined the influence of spatio-temporal and operational variables on the probability of vessels to experience interactions. Killer whales interactions occurred during 58.4% and 21.2% of all fishing days, and over 94% and 47.4% of the fishing area for both fisheries, respectively. In south-eastern Australia, the probability of occurrence of killer whale interactions during fishing days varied seasonally with a decrease in spring, increased with the daily fishing effort and decreased with the distance travelled by the vessel between fishing days. In Amsterdam/St. Paul, this probability was only influenced by latitude, with an increase in the southern part of the area. Together, these findings document two previously unreported cases of high killer whale depredation, and provide insights on ways to avoid the issue. The study also emphasizes the need to further examine the local characteristics of fisheries and the ecology of local depredating killer whale populations in as important drivers of depredation.

Diversity of Mesopelagic Fishes in the Southern Ocean - A Phylogeographic Perspective Using DNA Barcoding

Small mesopelagic fish are ubiquitous in the ocean, representing an important trophic link between zooplankton and tertiary consumers such as larger fish, marine mammals and birds. Lanternfishes (Myctophidae) are common worldwide as well as in the Southern Ocean. However, only 17 of the approximately 250 myctophid species occur exclusively in sub-Antarctic or Antarctic waters. It is unclear whether they colonized these latitudes once and diversified from there, or whether multiple colonization events took place in which multiple ancestral phenotypes entered the Southern Ocean at various times. Phylogeographic patterns have been investigated for individual myctophid species, but so far no study has compared species across the Southern Ocean. Here, we present a dataset with previously unpublished cytochrome c oxidase I (COI; n = 299) and rhodopsin (rh1; n = 87) gene sequences from specimens collected at various locations in the Southern Ocean. Our data extend the DNA barcode library of Antarctic mesopelagic fish substantially. Combined morphological and molecular taxonomy lead to confident species level identification in 271 out of 299 cases, providing a robust reference dataset for specimen identification, independently of incomplete morphological characters. This is highly topical in light of prospective ecological metabarcoding studies. Unambiguous sequences were subsequently combined with publicly available sequences of the global DNA barcode library yielding a dataset of over 1000 individuals for phylogenetic and phylogeographic inference. Maximum likelihood trees were compared with results of recent studies and with the geographical origin of the samples. As expected for these markers, deep phylogenetic relationships remain partially unclear. However, COI offers unmatched sample and taxon coverage and our results at the subfamily to genus level concur to a large extent with other studies. Southern Ocean myctophids are from at least three distant subfamilies suggesting that colonization has occurred repeatedly. Overall, spatial divergence of myctophids is rare, potentially due to their enormous abundance and the homogenizing force of ocean currents. However, we recommend further investigation of the phylogenetic position of Symbolophorus boops and highlight potential (pseudo-)cryptic or unrecognized species in Gymnoscopelus bolini, Lampanyctus achirus, and the non-myctophid genus Bathylagus.