Counting whales in a challenging, changing environment
Williams, R. ; Kelly, N. ; Boebel, O. ; Friedlaender, A. ; Herr, H. ; Kock, K.H. ; Lehnert, L.S. ; Maksym, T. ; Roberts, J. ; Scheidat, M. ; Siebert, U. ; Brierley, A. - \ 2014
Scientific Reports 4 (2014). - ISSN 2045-2322 - 6 p.
antarctic sea-ice - abundance - extent - ocean - krill - ecosystem - shelf - edge
Estimating abundance of Antarctic minke whales is central to the International Whaling Commission's conservation and management work and understanding impacts of climate change on polar marine ecosystems. Detecting abundance trends is problematic, in part because minke whales are frequently sighted within Antarctic sea ice where navigational safety concerns prevent ships from surveying. Using icebreaker-supported helicopters, we conducted aerial surveys across a gradient of ice conditions to estimate minke whale density in the Weddell Sea. The surveys revealed substantial numbers of whales inside the sea ice. The Antarctic summer sea ice is undergoing rapid regional change in annual extent, distribution, and length of ice-covered season. These trends, along with substantial interannual variability in ice conditions, affect the proportion of whales available to be counted by traditional shipboard surveys. The strong association between whales and the dynamic, changing sea ice requires reexamination of the power to detect trends in whale abundance or predict ecosystem responses to climate change.
Recent trends in sea surface temperature off Mexico
Lluch-Cota, S.E. ; Tripp-Valdéz, M. ; Lluch-Cota, D.B. ; Lluch-Belda, D. ; Verbesselt, J. ; Herrera-Cervantes, H. ; Bautista-Romero, J. - \ 2013
Atmósfera 26 (2013)4. - ISSN 0187-6236 - p. 537 - 546.
california current system - variability - atlantic - climate - oscillation - pacific - hypoxia - shelf
Changes in global mean sea surface temperature may have potential negative implications for natural and socioeconomic systems; however, measurements to predict trends in different regions have been limited and sometimes contradictory. In this study, an assessment of sea surface temperature change signals in the seas off Mexico is presented and compared to other regions and the world ocean, and to selected basin scale climatic indices of the North Pacific, the Atlantic and the tropical Pacific variability. We identified eight regions with different exposure to climate variability: In the Pacific, the west coast of the Baja California peninsula with mostly no trend, the Gulf of California with a modest cooling trend during the last 20 to 25 years, the oceanic area with the most intense recent cooling trend, the southern part showing an intense warming trend, and a band of no trend setting the boundary between North-Pacific and tropical-Pacific variability patterns; in the Atlantic, the northeast Gulf of Mexico shows cooling, while the western Gulf of Mexico and the Caribbean have been warming for more than three decades. Potential interactions with fisheries and coastal sensitive ecosystems are discussed
Foraging black-browed albatrosses target waters overlaying moraine banks-a consequence of upward benthic-pelagic coupling?
Wakefield, E.D. ; Phillips, R.A. ; Belchier, M. ; Aarts, G. ; Mackenzie, M. ; McConnell, B.J. - \ 2012
Antarctic Science 24 (2012)3. - ISSN 0954-1020 - p. 269 - 280.
south-georgia - shag rocks - shelf - segregation - seabirds - ocean - diet - sea - chrysostoma - strategies
Wide-ranging, surface-feeding pelagic seabirds are the most numerous functional group of birds in the Southern Ocean. The mesoscale habitat use of these birds is increasingly being quantified by relating their movements to remotely sensed, near surface properties of the ocean. However, prey availability at the sea surface may also be determined by habitat characteristics not measurable from space. For instance, benthic-pelagic coupling, which occurs when seabed processes affect productivity in the epipelagic zone, can link benthic habitat type to availability of surface prey. We combined acoustically derived maps of the substrate of the South Georgia shelf with GPS tracking to quantify the sub-mesoscale habitat use of breeding black-browed albatrosses. We show that albatrosses preferentially used waters overlaying glacial moraine banks near the shelf edge and that this was unrelated to the presence of trawlers targeting mackerel icefish, which are also associated with these features. Stomach temperature profiles suggest that albatrosses primarily caught krill and fish over the banks.We hypothesize that black-browed albatrosses target waters overlaying moraine banks due to upward benthic-pelagic coupling, mediated by an increase in abundance of zooplankton such as Antarctic krill. Our findings suggest that the potential effects of such processes on pelagic seabird distribution warrant wider investigation.
Ecotypes as a concept for exploring responses to climate change in fish assemblage
Engelhard, G.H. ; Ellis, J.R. ; Payne, M.R. ; Hofstede, R. ter; Pinnegar, J.K. - \ 2011
ICES Journal of Marine Science 68 (2011)3. - ISSN 1054-3139 - p. 580 - 591.
long-term changes - marine plankton ecosystems - north-sea - trophic level - coastal fish - community - shelf - size - common - variability
How do species-rich fish assemblages respond to climate change or to other anthropogenic or environmental drivers? To explore this, a categorization concept is presented whereby species are assigned with respect to six ecotype classifications, according to biogeography, horizontal and vertical habitat preference, trophic guild, trophic level, or body size. These classification schemes are termed ecotypology, and the system is applied to fish in the North Sea using International Bottom Trawl Survey data. Over the period 1977–2008, there were changes in the North Sea fish community that can be related to fish ecotypes. Broadly speaking, there were steady increases in abundance of species that were either Lusitanian, small-bodied, or low-/mid-trophic-level ecotypes, and generally declining or only marginally increasing trends of most Boreal, large-bodied, or high-trophic-level ecotypes or combinations of them. The post-1989 warm biological regime appears to have favoured pelagic species more than demersal species. These community-level patterns agree with the expected responses of ecotypes to climate change and also with anticipated vulnerability to fishing pressure
Do changes in environmental and fishing pressures impact marine communities? An empirical assessment
Rochet, M.J. ; Trenkel, V.M. ; Carpentier, A. ; Coppin, F. ; Sola, L.G. ; Leaute, J.P. ; Mahe, J.C. ; Maiorano, P. ; Mannini, A. ; Murenu, M. ; Piet, G.J. ; Politou, C.Y. ; Reale, B. ; Spedicato, M.T. ; Tserpes, G. ; Bertrand, J.A. - \ 2010
Journal of Applied Ecology 47 (2010)4. - ISSN 0021-8901 - p. 741 - 750.
compensatory dynamics - indicators - shelf - eutrophication - ecosystems - mechanisms - management - fisheries - metrics - trends
1. The development of ecosystem approaches to environmental management implies the need to account for multiple pressures on ecosystems. Trends in multiple metrics that respond differently to changes in major environmental pressures need to be combined to evaluate the impacts of fishing and environmental changes on fish communities. 2. An exploited fish community is viewed as a three-level food chain in which the two upper levels, or functional groups, are targeted by fishing fleets, while the lowest level is subject to environmental variation. Qualitative modelling is used to predict changes at the two upper levels, that is, top-down vs. bottom-up perturbations. Abundance and length metrics are calculated from survey data for 14 Mediterranean and East-Atlantic groundfish shelf communities at both population and functional group levels. The joint likelihood of time trends in metrics is used to evaluate the evidence for different causes of changes. 3. A wide diversity of impacts is found to have equal evidence at the population level within each community. Consistency between the impacts identified and changes in pressures known from independent information is found at the functional group and community level. The results suggest that there is some compensation between species within functional groups. 4. Synthesis and applications. The method can be used to conduct an integrated assessment of community dynamics subject to multiple pressures. Joint trends in metrics provide evidence of which known pressures are having an impact on the community, and thus, which management actions should be taken to mitigate these changes.
Sympagic occurrence of Eusirid and Lysianassoid amphipods under Antarctic pack ice
Krapp, R.H. ; Berge, J. ; Florentino De Souza Silva, A.P. ; Gulliksen, B. ; Werner, I. - \ 2008
Deep-Sea Research. Part II, tropical studies in oceanography 55 (2008)8-9. - ISSN 0967-0645 - p. 1015 - 1023.
sea-ice - weddell sea - perdentatus chevreux - community structure - 1912 crustacea - mcmurdo sound - micronekton - shelf
During three Antarctic expeditions (2004, ANT XXI-4 and XXII-2; 2006, ANT XXIII-6) with the German research icebreaker R/V Polarstern, six different amphipod species were recorded under the pack ice of the Weddell Sea and the Lazarev Sea. These cruises covered Austral autumn (April), summer (December) and winter (August) situations, respectively. Five of the amphipod species recorded here belong to the family Eusiridae (Eusirus antarcticus, E. laticarpus, E. microps, E. perdentatus and E. tridentatus), while the last belongs to the Lysianassidea, genus Cheirimedon (cf. femoratus). Sampling was performed by a specially designed under-ice trawl in the Lazarev Sea, whereas in the Weddell Sea sampling was done by scuba divers and deployment of baited traps. In the Weddell Sea, individuals of E. antarcticus and E. tridentatus were repeatedly observed in situ during under-ice dives, and single individuals were even found in the infiltration layer. Also in aquarium observations, individuals of E. antarcticus and E. tridentatus attached themselves readily to sea ice. Feeding experiments on E. antarcticus and E. tridentatus indicated a carnivorous diet. Individuals of the Lysianassoid Cheirimedon were only collected in baited traps there. Repeated conventional zooplankton hauls performed in parallel to this study did not record any of these amphipods from the water column. In the Lazarev Sea, E. microps, E. perdentatus and E. laticarpus were regularly found in under-ice trawls. We discuss the origin and possible sympagic life style of these amphipods.
Potential pressure indicators for fishing, and their data requirements
Piet, G.J. ; Quirijns, F.J. ; Robinson, L. ; Greenstreet, S.P.R. - \ 2007
ICES Journal of Marine Science 64 (2007)1. - ISSN 1054-3139 - p. 110 - 121.
ecosystem-based management - marine capture fisheries - southern north-sea - competitive interactions - community indicators - temporal trends - impact - mortality - metrics - shelf
Indicators of fishing pressure are necessary to support an ecosystem approach to fisheries management (EAFM). We present a framework that distinguishes four levels of pressure indicators that move from being a simple description of anthropogenic activity to more precisely describing the actual pressure on the ecosystem and its components, but which require increasingly more information to be quantified. We use the example of the Dutch beam trawl fleet in the North Sea to compare these pressure indicators, as the level of information used is increased. The first level is that of fleet capacity (e.g. number of vessels), the second is fishing effort, usually expressed as the number of hours fishing or days at sea, the third incorporates fishing parameters such as the proportion of time actually spent fishing, fishing speed, or gear characteristics, e.g. the size of the beam trawl in order to determine the frequency with which an area is fished, and at the fourth level, the most informative measure of fishing pressure, annual fishing mortality, is available for a few commercial species from stock assessments. For other species, it can be calculated from the lower level pressure indicators through the incorporation of the chance of individuals of a species coming into contact with the fishing gear and the encounter mortality, which is the portion of mortality caused by the passing of the gear. Comparison of trends and absolute values shows that the pressure indicators at different levels differ considerably in their description of both present and historical fishing impact in the North Sea. Therefore, for an EAFM, we advise using the highest level pressure indicator that can be obtained with the data available.
Cumulative impacts of seabed trawl disturbance on benthic biomass, production, and species richness in different habitats
Hiddink, J.G. ; Jennings, S. ; Kaiser, M.J. ; Queiros, A.M. ; Duplisea, D.E. ; Piet, G.J. - \ 2006
Canadian Journal of Fisheries and Aquatic Sciences 63 (2006)4. - ISSN 0706-652X - p. 721 - 736.
soft-sediment communities - mobile fishing gear - southern north-sea - ecosystem function - coral-reefs - macrofauna - shelf - size - bioturbators - assemblages
Bottom trawling causes widespread disturbance of sediments in shelf seas and can have a negative impact on benthic fauna. We conducted a large-scale assessment of bottom trawl fishing of benthic fauna in different habitats, using a theoretical, size-based model that included habitat features. Species richness was estimated based on a generalized body mass versus species richness relationship. The model was validated by sampling 33 stations subject to a range of trawling intensities in four shallow, soft sediment areas in the North Sea. Both the model and the field data demonstrated that trawling reduced biomass, production, and species richness. The impacts of trawling were greatest in areas with low levels of natural disturbance, while the impact of trawling was small in areas with high rates of natural disturbance. For the North Sea, the model showed that the bottom trawl fleet reduced benthic biomass and production by 56% and 21%, respectively, compared with an unfished situation. Because of the many simplifications and assumptions required to synthesize these data, additional work is required to refine the model and evaluate applicability in other geographic areas. Our model enables managers to understand the consequences of altering the distribution of fishing activities on benthic production and hence on food web processes.
Late-Holocene evolution of the Mahakam delta, East Kalimantan, Indonesia
Storms, J.E.A. ; Hoogendoorn, R.M. ; Dam, R.A.C. ; Hoitink, A.J.F. ; Kroonenberg, S.B. - \ 2005
Sedimentary Geology 180 (2005)3-4. - ISSN 0037-0738 - p. 149 - 166.
brahmaputra river system - ganges-brahmaputra - sediment transport - subaqueous delta - shelf - ocean - quaternary - record
The late-Holocene Mahakam delta, located along the tropical eastern shore of Kalimantan, Indonesia, is considered to be a textbook example of a mixed tide-fluvial dominated delta system. The delta prograded about 60 km during the past 5000 years, which led to the development of a distinct network of distributary and tidal channels. Wave action is low due the limited fetch in the narrow strait of Makassar. Mahakam River discharge is about a quarter of the Mississippi River discharge and is characterized by absence of flood surges. Therefore, natural levees, crevasse splays and avulsions are absent in the delta plain. For the past four decennia, both modern and ancient Mahakam delta deposits have been studied in detail in order to better understand subsurface Miocene and Tertiary Mahakam deposits, which host large volumes of hydrocarbons. This study focuses on the dynamics and stratal patterns of delta plain, delta-front platform deposits and suspended sediments. Due to the predominance of semi-diurnal tides and the associated flow reversals, depositional patterns are highly variable which has resulted in the formation of characteristic sand-mud couplets. The distribution of the sand-mud couplets found in this study differs from previously proposed conceptual models. They are limited to the fluvial domain and form in the distributary channels (lateral channel bar) or at the fluvial dominated delta-front platform, which flanks the mouth bar deposits in offshore direction. The sand-mud couplets which formed as delta-front platform and lateral channel bar deposits are similar and can only be identified based on their 14C age. The sand content decreases significantly towards the tidal dominated areas due to limitation in transport capacity. Turbidity measurements taken in front of the river mouth also show rapid settlement of river plume sediments. Some 22 new AMS 14C dates show that late Holocene sea level history resembles the eustatic sea level curve giving a first approximation of the Late Holocene sea level history for East Kalimantan. The dates suggest that the progradational delta system evolved under conditions of slowly rising sea level, which compares well to the eustatic sea level curve. In addition, calculated averaged deposition rates of the sand-mud couplets indicate that deposition is driven by the spring-neap tide cycles instead of the daily tidal cycle