Offshore Seamounts Research Articles

Insights into swordfish (Xiphias gladius) movement patterns and habitat utilization off the coast of northern Chile

This study reports on the fine-scale movements of swordfish (Xiphias gladius) tagged off of the Antofagasta region of northern Chile, where harpoon fishing operations date back more than seven millenia. The study was conducted within a highly productive swordfish foraging area where movements and habitat use remain poorly characterized. Swordfish were outfitted with both data storage and satellite-linked archival tags scheduled for short (<30 days) and longer-term (>100 days) data collection. All tags were deployed on basking swordfish using harpoon-based methods across two field seasons in March 2019 and April 2022 around oceanic fronts and offshore seamounts. Fine-scale depth and temperature data were recorded over 145 days from four adult swordfish (100-200 kg). Swordfish exhibited regionally unique diurnal behaviors with greater average daytime depths than those recorded at night (78.0 ± 66.5 and 12.7 ± 4.9 m, respectively). The average daytime depths were shallower than those previously documented for other Pacific regions, including Chile's offshore waters. Daytime basking was observed on 76% of the daily records (110 out of 145 days) and accounted for approximately 12% of the collective daylight hours. Findings align with previous swordfish tagging studies and suggest that depth distribution patterns vary considerably depending on regional oceanographic conditions. Movement data are compared with previous studies, and we discussed relative to regional fishing operations.

An expanded Smithian–Spathian (Lower Triassic) boundary from a reefal build‐up record in Oman: implications for conodont taxonomy, high‐resolution biochronology and the carbon isotope record

AbstractSome 2.7 myr after the Permian–Triassic boundary mass extinction, a stepwise extinction of the nekton (ammonoids and conodonts) ended at the Smithian–Spathian boundary (SSB) during an episode of climate cooling. SSB records from continental shelves are usually affected by an unconformity, suggesting a forced regression of glacio‐eustatic origin. Here, we document a new 30‐m‐thick SSB section from Jebel Aweri (Batain Plain, Oman) that provides an exceptionally complete and expanded record preserved in an exotic block. Most of this SSB section consists of microbial boundstone build‐ups with a framework of metazoan bioclasts that formed in shallow water on an offshore seamount. In Wadi Musjah (Hawasina nappes, Oman), another exotic block records the SSB in a deeper water setting represented by Hallstatt‐type facies. These two sections provide a unique perspective on the early Spathian rapid re‐diversification of conodonts. They led to a thorough revision of conodont taxonomy around the SSB and to the construction of the highest resolution biochronological scheme for this time interval in the Tethys. A total of five SSB sections from Oman representing both offshore seamounts and lower slope deposits were included in a high‐resolution, quantitative unitary associations (UA) analysis. The resulting 8 conodont biozones are intercalibrated with ammonoid zones and with the carbonate carbon isotope record ultimately placing the SSB in the interval of separation between UAZ3and UAZ4. Only the association ofNovispathodus pingdingshanensiswithIcriospathodus crassatuscan be used to unambiguously characterize the base of the Spathian.

A multi-method characterization of Elasmobranch & Cheloniidae communities of the north-eastern Red Sea and Gulf of Aqaba.

The Red Sea is particularly biodiverse, hosting high levels of endemism and numerous populations whose extinction risk is heightened by their relative isolation. Elasmobranchs and sea turtles have likely suffered recent declines in this region, although data on their distribution and biology are severely lacking, especially on the eastern side of the basin in Saudi Arabian waters. Here, we present sightings of elasmobranchs and sea turtles across the north-eastern Red Sea and Gulf of Aqaba collected through a combination of survey methods. Over 455 survey hours, we recorded 407 sightings belonging to 26 elasmobranch species and two sea turtle species, more than 75% of which are of conservation concern. We identified 4 species of rays and 9 species of sharks not previously recorded in Saudi Arabia and report a range extension for the pink whipray (Himantura fai) and the round ribbontail ray (Taeniurops meyeni) into the Gulf of Aqaba. High density of sightings of conservation significance, including green and hawksbill sea turtles and halavi guitarfish were recorded in bay systems along the eastern Gulf of Aqaba and the Saudi Arabian coastline bordering the north-eastern Red Sea, and many carcharhinid species were encountered at offshore seamounts in the region. Our findings provide new insights into the distribution patterns of megafaunal assemblages over smaller spatial scales in the region, and facilitate future research and conservation efforts, amidst ongoing, large-scale coastal developments in the north-eastern Red Sea and Gulf of Aqaba.

Brachiopod Fauna from the Deep Mediterranean Sea: Distribution Patterns and Ecological Preferences

Compared to their fossil counterparts, living brachiopods are investigated far less often, due to their occurrence in remote environments such as dark caves or deep environments. Due to the scarcity of studies targeting in situ brachiopods’ populations, large-scale information on their distribution and ecological preferences is still lacking, especially on hardgrounds. The extensive employment of remotely operated vehicles (ROVs), however, has opened up the chance to better explore this taxon’s diversity and ecology in the mesophotic and bathyal zones. The analysis of over 600 h of video footage collected from 624 sites, from 40 m to 1825 m, located along the Ligurian and Tyrrhenian coasts of Italy and the Sicily Channel, allowed for a large-scale investigation. The four identified species, Novocrania anomala, Gryphus vitreus, Megerlia truncata and Terebratulina retusa, emerged as common macrofaunal components of the explored habitats, especially between 150 m and 250 m, with high occurrences in the northern areas, especially on offshore seamounts. All species can form dense aggregations of individuals, with M. truncata showing the densest populations on steep rocky terraces (up to 773 individuals m−2). Except for G. vitreus, the only species also recorded on soft bottoms, the others were found exclusively on hardgrounds, with N. anomala showing a peculiar ability to exploit anthropogenic substrates such as terracotta amphorae. No stable species-specific associations were noted, even if numerous species were frequently observed together. Although brachiopods do not show the conspicuous tridimensionality of large filter-feeders, their substrate occupancy and their role in pelagic–benthic processes support their importance in deep-sea Mediterranean ecosystems.

Basin-scale occurrence and distribution of mesophotic and upper bathyal red coral forests along the Italian coasts

The analysis of 879 ROV dives carried out along the Italian coasts on hard substrata at mesophotic and upper bathyal depths (40-775 m) allowed us to evaluate the current basin-scale presence, relative abundance, bathymetric limits, and habitat preferences of one of the most charismatic Mediterranean habitat-former anthozoan species, Corallium rubrum (Linnaeus, 1758). The species is widespread, and its occurrence ranged from 13% of the explored sites in Ionian Calabria to a hotspot of approximately 80% in Sardinia. Population relative densities were generally low (< 10 colonies m-2), except along the Sardinian coasts and in some areas along the Apulian coast. Almost no red coral colonies were observed between 60 m and 590 m in the nine explored offshore seamounts in the Ligurian and Tyrrhenian Seas. A distinctive coastal distribution discontinuity was found in the Ionian Sea. The optimum bathymetric distribution was between 75 m and 125 m, and no colonies were found below 247 m. Red coral colonies showed a preference for biogenic habitats dominated by crustose coralline algae (CCA) and vertical substrata. The species was absent on iron wrecks. Corallium rubrum disappeared from 14% of the historical fishing banks, while it was confirmed in 86% of them, some of which have been deeply harvested in the past. In particular, the still flourishing Sardinian populations could be supported by the high reproductive potential and favourable hydrodynamic conditions in the area.

Diversity and abundance of heterobranchs (Mollusca, Gastropoda) from the mesophotic and bathyal zone of the Mediterranean Sea

The occurrence, relative abundance and bathymetric distribution of the deep Mediterranean heterobranch fauna were evaluated as a result of an extensive visual census down to 1825 m depth, carried out along the western Italian coasts, covering a latitudinal range of about 600 nautical miles. Observations were conducted using Remotely Operated Vehicles (ROVs) in 551 sites, focusing on the deepest part of the continental shelf, the shelf edge and the upper bathyal zone. The analysis of over 508 hours of video footage and more than 27,000 high-resolution photographs allowed to explore about 594,000 m2 of rocky outcrops and nearby soft seafloors in four main coastal areas (Ligurian Sea, north-central Tyrrhenian Sea, southern Tyrrhenian Sea, and Sicily Channel) and twelve offshore seamounts. Thirty-six species of heterobranchs, for a total of 559 records, were identified. Sixteen were only sporadically spotted (< 1% of the total observations), while three (Paraflabellina ischitana, Tritoniidae nd and Peltodoris atromaculata) contributed each for more than 10% of the records. An extension of the known Mediterranean bathymetric distribution was reported for 80% of the observed species, with many typically shallow-water taxa being also found in mesophotic environments (40–200 m). The observed marked decrease in diversity and abundance suggested that Mediterranean heterobranchs are mainly a coastal benthic group. From the geographical point of view, the heterobranch fauna present in the Ligurian Sea appeared significantly different from that observed in the Tyrrhenian Sea and the Sicily Channel, and this latitudinal pattern was discussed. Particular attention was given to single out the bathymetric distribution of the food sources of the most frequently observed species, supporting stenophagy as a limiting factor for their colonisation of the deep sea.

Cetacean occurrence in the Gulf of Alaska from long-term passive acoustic monitoring

The Gulf of Alaska is an important habitat for a diverse array of marine mammals, many of which were severely depleted by historical whaling. To study current cetacean distributions in this region, passive acoustic monitoring was used to detect species-specific call types between 2011 and 2015 at five locations spanning the continental shelf, slope, and offshore seamounts. Spatial and temporal detection patterns were examined for nine species to compare differences in behavior and habitat use. Mysticetes showed seasonal increases in calling that indicated possible behavioral shifts between feeding and breeding in blue (Balaenoptera musculus), fin (B. physalus), and humpback (Megaptera novaeangliae) whales, and matched known migration timing of gray whales (Eschrichtius robustus). Interannual changes in blue and fin whale calling may relate to the marine heat wave that began in 2013 and lasted through the end of the monitoring period. Odontocete detections revealed unique spatial distributions, with killer whales (Orcinus orca) most common on the continental shelf and sperm whales (Physeter macrocephalus) most common on the continental slope, where detections occurred year-round. Beaked whales showed both spatial and temporal separation: Baird’s beaked whale (Berardius bairdii) detections were highest at Quinn Seamount in the spring, Cuvier’s (Ziphius cavirostris) at Pratt Seamount in winter, and Stejneger’s (Mesoplodon stejnegeri) on the continental slope in the fall. The year-round presence of many species highlights the ecological importance of the Gulf of Alaska and the spatiotemporal information reported here should inform future conservation efforts.

Demersal fish assemblages on seamounts exploited by fishing in the Azores (NE Atlantic)

Seamount fish communities are susceptible to variations due to the oceanographic conditions and level of historical fishing effort. In the NE Atlantic, the Azores is considered an “oceanic seamount ecosystem area” because seamount concentration is high relative to other regions. Scientific information on seamounts in the Azores remains scarce and demersal fishery occurs mostly without any knowledge to endorse sustainable harvest strategies. To make available an important baseline information on dynamics of demersal fish populations inhabiting commercially exploited seamounts, the present study has as specific objectives to (a) describe the taxonomic composition of demersal fish assemblages on underwater mountains, (b) examine whether assemblages vary spatial and temporally, and (c) investigate what drives distributional patterns of species in terms of abundance and size composition. For this, three Azorean seamounts (Açores, Princesa Alice and Mar da Prata) exploited by bottom fishing were selected as case study areas. Data were obtained from scientific surveys and commercial fishery over the past c. 25 years. A total of 84 species from 45 families were identified. Sebastidae, Moridae, Sparidae and Centrophoridae were the most abundant families, mainly represented by Helicolenus dactylopterus, Mora moro, Pagellus bogaraveo and Deania profundorum, respectively. Fish assemblages were more distinguishable spatially than temporally. Depth was identified as the main factor responsible for these differences. The higher occurrence of shallow and intermediate (i.e., up to 600 m) habitats in Princesa Alice and Açores seems to favor the occurrence of a greater number of species and higher abundances in comparison to Mar da Prata. Phycis phycis, Pontinus kuhlii, H. dactylopterus, P. bogaraveo, Conger conger and M. moro were the species which primarily contributed to dissimilarities in assemblage structure among sample groups. Abundance indices and fish sizes showed a decreasing trend for many of these species, especially for those with sedentary behaviour inhabiting historically highly exploited seamount areas. These results highlighted the vulnerability of demersal fishes to the expansion of fishing effort in the offshore seamount areas. Spatial management of seamounts should be a priority being fish conservation balanced with strategies that support sustainable fisheries.

Description of Alpheus gallicus, a new deep-water snapping shrimp from Galicia Bank, northeastern Atlantic (Malacostraca, Decapoda, Alpheidae).

A new species of the snapping shrimp genus Alpheus Fabricius, 1798 is described based on material from Galicia Bank, an offshore seamount off northwestern Spain. The type series of Alpheus gallicus n. sp. was collected at a depth of 768-785 m, making it one of the deepest occurring snapping shrimps. The new species belongs to the Alpheus macrocheles species group and is morphologically most similar to several deep-water members of this group, viz. A. lentiginosus Anker Nizinski, 2011, A. platydactylus Coutière, 1897, A. romensky Burukovsky, 1990, as well as to the shallow-water A. macrocheles (Hailstone, 1835). The new species can be distinguished from all of them by some features on the minor cheliped and dactyli of the third to fifth pereiopods. In addition to morphology, DNA barcoding of the COI gene distinguished A. gallicus n. sp. from all related species with available barcode sequences.

Intra- and interspecific associations in two predatory reef fishes at a shallow seamount

The spatial dynamics of marine populations are shaped by habitat availability, environmental variability and individual interactions, particularly when multiple species share limited habitat such as patchy offshore reefs. The yellowmouth barracuda Sphyraena viridensis and the almaco jack Seriola rivoliana are the 2 most abundant bentho-pelagic reef predators in the Azores archipelago (central North Atlantic). They aggregate at shallow offshore seamounts, and largely share diet preferences, but very little is known about how habitat and resources are shared by these predators intra- and inter-specifically. Here we use long-term (over 3 yr) passive acoustic telemetry to investigate the patterns of activity, space use and associative behaviour at an isolated, small shallow seamount. By quantifying fine-scale spatiotemporal overlaps and performing null model randomization tests, we found evidence of non-random associations, mostly between conspecifics of both species, as well as shifts in diel and seasonal patterns of space occupancy. Both species were detected more often during spring, and appear to be more active during daytime, suggesting the absence of fine-scale temporal habitat partitioning. Additionally, we found evidence of size-dependent spatial behaviour in almaco jack, with similarly sized individuals co-occurring more often and larger specimens being more infrequently detected. This study quantitatively assesses individual associations using solely presence-absence data collected through passive acoustic telemetry, showing the potential of this approach in a broader application to a significant number of past and ongoing studies, even if many were not originally designed to study this important aspect of fish ecology.

Marine mammal distribution in the Gulf of Alaska from long-term passive acoustic monitoring

The Gulf of Alaska is an important habitat for a diverse array of marine mammals. Conservation of these populations requires understanding how they utilize different habitats. Passive acoustic monitoring can be used to study marine mammal distributions because the unique call types produced by many species are well documented. Between 2011 and 2015, a total of 3793 days of recordings were collected from autonomous acoustic recorders at five locations broadly distributed around the continental shelf, slope, and offshore seamounts in the Gulf of Alaska. The spatial and temporal patterns of seven cetacean species were examined and differences in habitat use and behavior were compared. Inshore habitats featured higher detections of humpback (Megaptera novaeangliae) and gray (Eschrichtius robustus) whales, while blue (Balaenoptera musculus) and sperm (Physeter macrocephalus) whales were more commonly detected offshore. The presence of most species was seasonal, with peak calling in spring and summer for gray and sperm whales, and fall and winter for fin (B. physalus) and humpback whales. Call type distributions within a species differed spatially for fin and killer (Orcinus orca) whales, and seasonally for blue whales. Spatial differences may indicate prey preferences, while seasonal changes are likely related to behavioral shifts from feeding to mating.

Post-release survivorship and movements of bigeye thresher sharks, Alopias superciliosus, following capture on deep-set buoy gear

The bigeye thresher shark (Alopias superciliosus) is a large pelagic predator routinely caught in a new deep-set fishery off California. Deep-set buoy gear (DSBG) was recently developed to selectively target swordfish (Xiphias gladius) at depth during the daytime and is currently being trialed by a limited fleet of vessels operating under an exempted fishing permit (EFP) issued through the National Marine Fishery Service (NMFS) and Pacific Fisheries Management Council (PFMC). Although marketable, bigeye thresher sharks (BETS) are often released or discarded to conserve limited hold space for more valuable catch. This study outfitted BETS with pop-up satellite archival transmitters (PSATs) programmed for 30-day deployments to evaluate acute post-release survival in the DSBG fishery and begin to understand depth and temperature distribution for this poorly known species. Fourteen BETS (43–93 kg) were tagged from 2016 to 2018 with PSATs (Wildlife Computers sPATs and MiniPATs) following fight times that ranged from 15 to 171 min. Out of the 14 deployments, twelve individuals survived the acute effects of capture, one BETS died shortly after release and one individual was preyed upon 6 h after release. Given the lack of information surrounding the predation induced mortality, two survivorship estimates are provided, one that includes the event as a mortality resultant of the capture event (86% survivorship) and one that excludes the event from the analysis (92% survivorship). All surviving BETS exhibited consistent diurnal dive patterns in which the sharks remained below the thermocline during the day and within the mixed layer at night. Mean daytime depths ranged from 250 to 439 m, while mean nighttime depths ranged from 20 to 106 m. Daytime temperatures at depth ranged from 6 to 10 °C with the lowest temperature value (6.0 °C) recorded on the deepest dive (548 m). For all BETS, maximum night temperatures averaged from 22.5 to 25.1 °C. Two tagged individuals remained proximal to the study area (<150 km) with others moving up to >1300 km from the tagging site (mean = 1009 ± 455 km). Mean daily rates of horizontal movement ranged from 3.4 to 41.6 km day−1. The most common movement trend entailed BETS moving in a southerly direction towards a series of offshore seamounts along southern Baja California, Mexico (22°-26 °N and 114°-126 °W), a purported offshore corridor for other large pelagic sharks of the eastern Pacific.

Modelling the environmental niche space and distributions of cold-water corals and sponges in the Canadian northeast Pacific Ocean

Cold-water coral and sponge (CWCS) communities are important indicators of vulnerable marine ecosystems (VMEs) and are used to delineate areas for marine conservation and fisheries management. Although the northeast Pacific region of Canada (NEPC) is notable for having unique CWCS assemblages and is the location of >80% of Canadian seamounts, the extent of potential CWCS-defined VMEs in this region is unknown. Here, we used a diverse set of environmental data layers (n=30) representing a range of bathymetric derivatives, physicochemical variables, and water column properties to assess the primary factors influencing the niche separation and potential distributions of six habitat-forming groups of CWCS in the NEPC (sponge classes: Hexactinellida, Demospongiae; coral orders: Alcyonacea, Scleractinia, Antipatharia, Pennatulacea). The primary environmental gradients that influence niche separation among CWCS are driven by total alkalinity, dissolved inorganic carbon, and dissolved oxygen. Significant niche separation among groups indicates CWCS to be primarily specialists occurring in rare habitat conditions in the NEPC. Species distribution models (SDMs) developed for each CWCS group shared severely low dissolved oxygen levels ([O2] < 0.5 ml L−1) as a top predictor for habitat suitability in the NEPC. Niche separation is further emphasized by differences in the model-predicted areas of suitable habitat among CWCS groups. Although niches varied among taxa, the general areas of high habitat suitability for multiple CWCS groups in the NEPC occurred within the 500–1400 m bottom depth range which is strongly associated with the extensive oxygen minimum zone (OMZ) characterizing this region. As a result, the largest continuous area of potential CWCS habitat occurred along the continental slope with smaller, isolated patches also occurring at several offshore seamounts that have summits that extend into OMZ depths. Our results provide insight into the factors that influence the distributions of some of the most important habitat-forming taxa in the deep ocean and create an empirical foundation for supporting cold-water coral and sponge conservation in the NEPC.

Massive spawning behavior of the triplespine deepwater cardinalfish Sphyraenops bairdianus Poey, 1861 observed on an offshore sea mount in the West Mariana Ridge

Using a hydrographic echo sounder, we encountered an animal aggregation on a sea mount summit (350 m deep) at the West Mariana Ridge (14°07’ N, 142°48′ E). The aggregation suddenly ascended from the summit at civil dawn, and we were able to capture the ascending aggregation at the next dawn using a large midwater trawl net. Hundreds of fishes captured were determined to be Sphyraenops bairdianus (Poey, 1861). Hydrated eggs in the ovary were histologically confirmed, indicating that this species performed a massive spawning associated with an offshore sea mount and sunrise.

New data from Oman indicate benthic high biomass productivity coupled with low taxonomic diversity in the aftermath of the Permian–Triassic Boundary mass extinction

A new Early Triassic marine fauna is described from an exotic block (olistolith) from the Ad Daffah conglomerate in eastern Oman (Batain), which provides new insights into the ecology and diversity during the early aftermath of the Permian–Triassic Boundary mass extinction. Based on conodont quantitative biochronology, we assign a middle Griesbachian age to the upper part of this boulder. It was derived from an offshore seamount and yielded both nektonic and benthic faunas, including conodonts, ammonoids, gastropods and crinoid ossicles in mass abundance. This demonstrates that despite the stratigraphically near extinction at the Permian–Triassic Boundary, Crinoidea produced enough biomass to form crinoidal limestone as early as middle Griesbachian time. Baudicrinus, previously placed in Dadocrinidae, is now placed in Holocrinidae; therefore, Dadocrinidae are absent in the Early Triassic, and Holocrinidae remains the most basal crown-group articulates, originating during the middle Griesbachian in the Tethyan Realm. Abundant gastropods assigned to Naticopsis reached a shell size larger than 20 mm and provide another example against any generalized Lilliput effect during the Griesbachian. Whereas the benthic biomass was as high as to allow the resumption of small carbonate factories, the taxonomic diversity of the benthos remained low compared to post-Early Triassic times. This slow benthic taxonomic recovery is here attributed to low competition within impoverished post-extinction faunas.

Movements and behaviors of swordfish Xiphias gladius in the United States Pacific Leatherback Conservation Area

AbstractThis study reports on the movements of swordfish tagged within the Pacific Leatherback Conservation Area (PLCA), an expansive region (&gt;500,000 km2) off the U.S. West Coast that has been seasonally restricted to drift‐gillnet fishing since 2001 to reduce leatherback sea turtle (Dermochelys coricea) interactions. Thirteen swordfish were outfitted with satellite‐linked archival tags scheduled for short (2–20 days, n = 11) and longer‐term (150 days, n = 2) data collection. All tags were deployed on basking swordfish using traditional harpoon‐based methods during the fall of 2012–2013, near offshore seamounts (35.6°N/122.9°W to 37.4°N/123.5°W). Depth and temperature data from 11 swordfish (~90 to 150 kg) resulted in &lt;251 days of movement information from the PLCA region. All tagged individuals exhibited surface‐oriented nocturnal movements, spending &gt;99% of the night above the average thermocline depth (37.5 m), with an average night depth of 8.3 ± 1.6 m. Daytime depth distribution was greater and more variable (mean 107.1 ± 21.2 m), with fish primarily displaying three behavioral patterns: (i) basking activity, 16.7% of the day, (ii) a mixed‐layer distribution between 3 m and the thermocline (26.8% of the day), and (iii) prolonged dives below the thermocline, 56.5% of the day. For seven of the tracks, daytime basking rates increased when thermocline depth was &lt;37 m. As fish moved offshore, there was less variability in vertical movements with a reduction in both basking activity and mixed layer occupancy, as well as an increase in average daytime depth. These data are discussed with respect to the potential development of alternative fishery options for the PLCA.

The impacts of deep-sea fisheries on benthic communities: a review

AbstractDeep-sea fisheries operate globally throughout the world's oceans, chiefly targeting stocks on the upper and mid-continental slope and offshore seamounts. Major commercial fisheries occur, or have occurred, for species such as orange roughy, oreos, cardinalfish, grenadiers and alfonsino. Few deep fisheries have, however, been sustainable, with most deep-sea stocks having undergone rapid and substantial declines. Fishing in the deep sea not only harvests target species but can also cause unintended environmental harm, mostly from operating heavy bottom trawls and, to a lesser extent, bottom longlines. Bottom trawling over hard seabed (common on seamounts) routinely removes most of the benthic fauna, resulting in declines in faunal biodiversity, cover and abundance. Functionally, these impacts translate into loss of biogenic habitat from potentially large areas. Recent studies on longline fisheries show that their impact is much less than from trawl gear, but can still be significant. Benthic taxa, especially the dominant mega-faunal components of deep-sea systems such as corals and sponges, can be highly vulnerable to fishing impacts. Some taxa have natural resilience due to their size, shape, and structure, and some can survive in natural refuges inaccessible to trawls. However, many deep-sea invertebrates are exceptionally long-lived and grow extremely slowly: these biological attributes mean that the recovery capacity of the benthos is highly limited and prolonged, predicted to take decades to centuries after fishing has ceased. The low tolerance and protracted recovery of many deep-sea benthic communities has implications for managing environmental performance of deep-sea fisheries, including that (i) expectations for recovery and restoration of impacted areas may be unrealistic in acceptable time frames, (ii) the high vulnerability of deep-sea fauna makes spatial management—that includes strong and consistent conservation closures—an important priority, and (iii) biodiversity conservation should be &amp;gt; balanced with options for open areas that support sustainable fisheries.

Robust assessment of population trends in marine mammals applied to New Caledonian humpback whales

\textcopyright Inter-Research 2014.Estimating population trends for long-lived, migratory animals is challenging but essential for managing populations. Here we propose using a simple but potentially robust method, the direct estimation of population growth rate (PGR) from capture-recapture data. We considered an Endangered population of humpback whales Megaptera novaeangliae breeding and calving annually in the southern lagoon of New Caledonia. Studied since 1996, this population is known to exhibit a strong signal of transience, i.e. the presence of individuals that pass through the sampling area once, inducing detection heterogeneity. Another difficulty is that a more recently discovered second breeding and calving habitat (offshore seamounts to the south) has been surveyed with less intensity. Current direct PGR estimation models cannot deal with spatial sampling heterogeneity. In order to assess the reliability of the proposed method - in general and for our population in particular - we evaluated its robustness using simulations: first, when there are transient individuals; then, when the study area is split into 2 unequally sampled parts. We found no bias in PGR in the presence of transients. The bias with 2 unequally sampled parts depends on the amount and direction of exchanges, but appears negligible in our case study. The constant yearly PGR of the New Caledonian humpback whale population at the level of the 2 habitats was estimated at 1.15 (95% CI 1.11-1.20), suggesting outside recruitment. Whenever capture-recapture is feasible, we recommend the Pradel approach to estimate the PGR, validated with appropriate simulations, in order to assess population welfare.

Cold‐water coral habitats on seamounts: do they have a specialist fauna?

ABSTRACTAim The large biogenic structures formed by colonial cold‐water scleractinian corals provide valuable habitat for marine invertebrates on seamounts and the continental slope of all world oceans. These patchily distributed long‐lived structures are easily damaged by several human activities, particularly bottom trawling for fish, and are potentially vulnerable to ocean acidification caused by climate change. Consequently, an important conservation question is whether these structures support a specialized invertebrate fauna restricted to these habitats. Here we investigate the relationship between structures formed by the coral Solenosmilia variabilis and its associated ophiuroid (brittlestar) fauna, one of the dominant components of deep‐sea ecosystems.Location Seafloor habitat around Southern Australia, New Zealand, and the Macquarie Ridge from 35 to 53° S and 117° E–176° W, 500–1500 m depth.Methods Data were derived from samples collected by numerous scientific expeditions to the study region. Because these samples were collected using a variety of gear and effort, a two‐step approach was used. First, the largest consistently collected data set (73 ophiuroid species from 59 samples) was assembled for multivariate analysis. ANOSIM was used to test for differences in ophiuroid community composition between Solenosmilia and non‐Solenosmilia habitat on seamounts and the continental slope, and SIMPER was used to identify species that characterized Solenosmilia habitat. Second, these results were validated against all known data to ensure that these characteristic species had not been found in non‐Solenosmilia habitat elsewhere.Results The ophiuroid assemblages from Solenosmilia habitat were distinct from those found on other habitats on the continental slope and offshore seamounts across the study region. Although a suite of ophiuroid species characterized Solenosmilia habitat, most have also been collected from dead coral or other rubble, suggesting a physical rather than biological association between the coral matrix and its associated invertebrate fauna.Main conclusions Despite the lack of an exclusive ophiuroid–coral relationship, cold‐water scleractinian coral remains the principal habitat for a number of ophiuroid species across southern Australia and New Zealand. The slow growth rate of the coral and the low dispersal potential of some associated species suggest that recovery of damaged cold‐water coral assemblages will be a long‐term process.

Oceanographic conditions in North and Northwest Iberia and their influence on the Prestige oil spill

Oceanographic conditions at the time of the Prestige oil spill (November 2002) and following months are analyzed based on a set of hydrographic cruises. The ship sank off one of the flanks of the Galician Bank, an offshore seamount, and a major oil spill drifted to the N and NW Iberian coast mainly driven by dominant winds. Coastal circulation was characterized by freshwater plumes and the poleward slope current, and could have affected the fate of the oil spill and influenced stranding places. Seasonal evolution of oceanographic conditions in this particular year is compared with the long-term average and reveals specific features that need to be taken into account in studies of the impact of the oil spill on populations. Spring conditions commenced earlier than other years in the Southern Bay of Biscay, contrastingly in western Iberia. The lack of subsurface intrusion of subtropical waters suggests a low intense penetration of the poleward current in Spanish Biscay slopes. In western Iberia, the slope poleward current observed in late autumn weakens and is exported off slope during upwelling pulses in the spring, with no strong intrusion of the poleward current on the slope at the time of the spring bloom. A description of current velocities near the wreck on the Galician Bank is obtained after the analysis of a mooring line.