Synthetic communication signals influence wild harbour porpoise (Phocoena phocoena) behaviour

We used our novel and programmable Porpoise Alarm (PAL, patd.) to synthesize life-like, electronic harbour porpoise communication signals based on those described for captive animals. In the Little Belt, Denmark, we employed PAL (source level 158 ± 1 dB p–p re 1 μPa@1 m; centroid frequency 133 ± 8.5 kHz) to synthesize three aggressive click train types termed “A”, “F3” and “M1” to naive, free-living harbour porpoises. Via theodolite tracking (372 h of total visual effort spread over 10 expeditions) we found that, depending on signal type, porpoises either avoid or become attracted to PAL: Signal types “A” and “F3” are slight deterrents, porpoises increasing minimum range (+23 to 32 m, respectively), whereas “M1” attracts porpoises, reducing range (by − 29 m). As determined via archival acoustic detectors (AADs), both signals “F3” and “M1” led the animals to significantly intensify their click rate (by +10% and 68%, respectively) while signal “A” led to a significant reduction ( − 59%). We propose that equipping fishing gear with PAL emitting signal “F3” could potentially reduce porpoise by-catch by increasing (1) awareness through enhanced echolocation and (2) distance to the nets. Detection probability and radius of PAL/AAD tandems could be improved by emitting signal “M1” to focus porpoise echolocation signals on the AAD. The signal may also be useful in luring animals away from hazards, which may be helpful for conservation measures prior to the onset of harmful acoustic activities such as pile-driving, seismic exploration or ammunition clearance

Eine Thünen-Evaluierung von fisch- und fischereibezogenen Indikatoren der EU Meeresstrategie-Rahmenrichtlinie (MSRL)

Dieser Bericht stellt ein Bewertungsverfahren für die nationalen Indikatoren der Meeresstrategie-Rahmenrichtlinie (MSRL) vor, welche fischökologische Aspekte der Meeresumwelt oder die Auswirkungen von Fischerei erfassen sollen. Die Bewertung der MSRL-Indikatoren wurde vorgenommen, um den derzeit noch stattfindenden Auswahlprozess und die Operationalisierung der Indikatoren durch eine fachliche Einschätzung zu unterstützen. Es wurden insgesamt 23 MSRL-Indikatoren nach einem international erprobten Bewertungssystem gegen 15 Kriterien bewertet. Diese Kriterien berücksichtigten die Datenqualität, die Management-Praktikabilität und die konzeptionellen Qualitäten jedes Indikators. Die 15 Kriterien erlaubten somit eine genauere Betrachtung möglicher Defizite und die gezielte Erarbeitung von Empfehlungen zur Verbesserung der vorgestellten Indikatoren. Die exemplarische Bewertung durch die sieben Thünen-Expertinnen und -Experten zeigte, dass Indikatoren aus dem Fischereimanagement und den fischereiwissenschaftlichen Forschungsreisen grundsätzlich sehr gut bewertet wurden. Dies liegt daran, dass viele Indikatoren aus dem Fischereimanagement schon seit Jahrzehnten etabliert sind, als wissenschaftlich abgesichert gelten, sowie einen hohen Grad internationaler Abstimmung und eine relativ gute Datengrundlage aufweisen. Die Bewertungen von Indikatoren zu dem Zustand von Nahrungsnetzen oder benthischen Lebensräumen, sowie der Beifangintensitäten von Seevögeln und Meeressäugetieren wurden als schlechter eingeschätzt. Dies lag zum einen an der bisher mangelhaften Festlegung von Zielvorgaben (benthische Lebensräume), unzureichenden bzw. unpräzisen technischen Beschreibungen der Indikatoren und ihrer Messgrößen (Nahrungsnetze), sowie fehlender internationaler Abstimmung (Nahrungsnetze & benthische Lebensräume). Für Beifänge von Seevögeln und Meeressäugetieren fiel die Bewertung aufgrund der geringen Datenverfügbarkeit negativ aus. Um die Indikatoren mit schlechter Bewertung zu operationalisieren, sollte die technische Entwicklung auf internationaler Ebene vorangetrieben (Nahrungsnetze) und die Datengrundlagedurch intensiviertes Monitoring verbessert werden (benthische Lebensräume, Beifangindikatoren). Ein wesentlicher Teil der ausstehenden Arbeiten betrifft Bewertungsmethoden, sowie Bestimmung und Festlegung von Grenz- bzw. Zielwerten. Zwar liegen für viele Indikatoren Bewertungrschläge aus der wissenschaftlichen Literatur vor, es bedarf aber einer finalen politischen Abstimmung

Trophic redundancy in benthic fish food webs increases with scarcity of prey items, in the Southern Baltic Sea

Bottom trawling is one of the main pressures on benthic ecosystems, directly impacting the targeted species and physically disturbing the seabed and the benthic invertebrate communities, in turn indirectly impacting benthivorous fish and the entire benthic food web structure and functioning. To predict the cascading effect of bottom trawling on benthic and demersal fish communities, it is crucial to understand the trophic interactions between benthic and demersal fish and benthic invertebrates. Here, we assessed the diet of benthic and demersal fish and the structure and functioning of the benthic food web in two areas in the German Baltic Sea, the Fehmarnbelt and the Odra Bank. The Fehmarnbelt benthic invertebrate community is characterized by a high number of species and biomass, contrary to the one on the Odra Bank which is species poor with high individual abundance but low biomass. We used mixing models based on stable isotopes of carbon and nitrogen combined with stomach content analyses to estimate the fish diet at both sites, and we used community-wide trophic indices, derived from stable isotopes to compare the structure and functioning of the fish benthic food webs. We show that fish in the Fehmarnbelt can chose preferential prey items, resulting in higher trophic diversity, contrary to fish on the Odra Bank, which feed on all available prey species, resulting in higher trophic redundancy. We found that the generalist behavior of fish on the Odra Bank is likely the result of scarcity in prey items, the benthic invertebrate community being species poor with high abundance of small individuals. We demonstrate that the differences in structure and functioning of the benthic fish food web between the two sites was mainly driven by differences in the characteristics of the benthic prey communities

Workshop on estimation of mortality of marine mammals due to bycatch (WKMOMA)

The Workshop on estimation of MOrtality of Marine MAmmals due to Bycatch (WKMOMA) addressed a special request from OSPAR regarding the bycatch mortality of marine mammals (harbour porpoise Phocoena phocoena; common dolphin Delphinus delphis; and grey seal Halicho-erus grypus) within the OSPAR maritime area. The objective of the workshop was to generate bycatch rates and associated confidence intervals for static and towed gears for relevant species within the three species assessment areas defined by OSPAR. Subsequently, the species-specific bycatch mortality estimates in the defined assessment area were requested. OSPAR provided thresholds for the relevant species/assessment units and ICES were tasked to compare the mortality estimates to the provided thresholds and identify any critical issues relevant for the comparison

Working group on bycatch of protected species (WGBYC 2021)

The Working Group on Bycatch of Protected Species (WGBYC) was established in 2007 and collates and analyses information from across the Northeast Atlantic and adjacent sea areas (Baltic, Mediterranean and Black Seas) related to the bycatch of marine mammals, seabirds, turtles, and sensitive fish species in commercial fishing operations. Sensitive fish species were not considered at the 2021 meeting pending approval from the ICES Advisory Committee (ACOM) on fish species lists of bycatch interest that were developed at the ICES Workshop on Fish of Conservation and Bycatch Relevance (WKCOFIBYC) in 2020. WGBYC seeks to describe and improve under-standing of the likely impacts of fishing activities on affected populations at biologically relevant scales, to inform on the suitability of existing at-sea monitoring programmes for the quantification of robust bycatch estimates, and to collate information on and coordinate bycatch mitigation efforts at an international scale. In 2021, the WG met by correspondence to address eight Terms of Reference (ToR), including a data scoping exercise as part of a special request on seabird bycatch from the North East Atlantic Fisheries Commission (NEAFC), which concluded that there was insufficient bycatch monitoring data from NEAFC waters to warrant further analyses at this time. The report also provides an overview of monitoring and fishing effort data contained in the WGBYC database for 2019 and 2020. This showed that during 2020, in most geographical areas of relevance, at-sea monitoring effort was significantly affected by the Covid-19 pandemic. Specific analyses were carried out to describe potential fisheries impacts (reported bycatch numbers, min/max bycatch rates and/or mortality estimates) for harbour seal in the Greater North Sea ecoregion and parts of the Baltic ecoregion, three turtle species in four Mediterranean ecoregions and in the Azores and Bay of Biscay and Iberian Coast ecoregions, and several seabird species in six ecoregions (Adriatic, Baltic, Bay of Biscay and Iberian Coast, Celtic Seas, Greater North Sea and Icelandic Waters). A risk-based approach, developed by WGBYC in 2020 to highlight monitoring gaps, was expanded using information from multiple sources and identified several high-risk métiers for bycatch which are relatively under-sampled by existing data collection programmes. Several members of WGBYC also participated simultaneously in the ICES Workshop on Estimation of Mortality of Marine Mammals due to Bycatch (WKMOMA) which ran over schedule due to data issues. Data used by WGBYC on fishing effort, at-sea monitoring effort and bycatch records are primarily acquired through an ICES dedicated data call which has been issued annually to all ICES member states since 2018 and all non-ICES EU coastal states from 2021. Although data quality and quantity are improving, WGBYC reiterate that significant gaps remain in data collection efforts and in data resolution, that limits the Working Group’s ability to provide useful assessments of the likely impacts of fishing activity across a wide range of protected species and areas. WGBYC note that broadscale low level monitoring programmes may be insufficient to highlight very rare bycatch occurrences for populations at low abundance and/or low susceptibility to by-catch, but which could have significant population levels impacts

Nutritional situation for larval Atlantic herring (Clupea harengus L.) in two nursery areas in thewestern Baltic Sea

The Greifswalder Bodden (GWB) is considered to be the most important spawning and nursery area for the western Baltic spring-spawning herring. However, the biotic and abiotic reasons for this are still unclear. Consequently, we investigated larval growth conditions in the GWB and in the Kiel Canal (KC), another nursery and spawning area of Baltic herring. We investigated prey quantity and quality [copepod abundance and essential fatty acid (EFA) concentration] as well as biochemically derived growth rates and fatty acid content of larval herring in spring 2011. A significant correlation between larval growth and larval EFA concentration could be observed in the GWB. The highest growth rates and EFA concentrations in the larval herring coincided with high food quality. Compensating effects of food quality on food quantity and vice versa could be observed in both the GWB and the KC. While larval growth rates in the KC were high early in the season, highest growth rates in the GWB were achieved late in the season. In conclusion, neither area was superior to the other, indicating similar growth conditions for larval herring within the region