HELCOM Core Indicator Report Structure - Pressure

Number of drowned mammals and waterbirds in fishing gear

Inhalt

Key message

Relevance of the core indicator

Policy relevance of the core indicator

Authors

Cite this indicator

Indicator concept

Environmental Target

Relevance of the indicator

Policy Relevance

Role of the pressure exerted though by-catch on the ecosystem

Assessment protocol

Results

Monitoring requirements

Monitoring methodology

Description of optimal monitoring,

Current monitoring

Description of data and confidence

Metadata

Confidence of indicator status

Arrangements for up-dating the indicator

Publications and archive

Printable version of the core indicator

Key message

The pressure core indicator is applicable in the whole Baltic Sea as it is known that birds and mammals are by-caught in the whole area. The indicator is relevant in all open water and in nearshore areas of the Baltic Sea.However no targeted monitoring is currently carried out and due to the resulting lack in monitoring data, it has not been possible to set an Environmental Target (ET) for the indicator and it is not possible to determine if the current rate of by-catch is within limits that enable reaching good environmental status (GES).

The core indicator follows the number of drowned marine mammals (cetaceans, seals and otters) and waterbirds (divers, grebes, cormorants, seaducks, auks) in fishing gears. The indicator is relevant in all open water and in nearshore areas of the Baltic Sea. Bycatch of harbour porpoises and seals is difficult to estimate and reliable studies are scarce,The increased mortality due to drowning in fishing gears but for harbour porpoise the bycatch in fishing gears is estimated to be the greatest source of mortality to the populations in the Baltic Sea and the number of drowned animals is believed to be above the environmental targets of the allowable mortality for this species. Drowning in fishing gear is also believed to be a primary pressure on the populations

Fishery bycatch is a high pressure to of long-tailed duck, scoters and some other waterbird species in wintering areas of high densities of waterfowl, and although a declining trend in numbers of by-caught birds has been detected in the . The bycatch rate has decreased during the last two decades this , but that is likely a result of declininged abundance of wintering waterbirds and not improved fishing practices.

However, current national discard/bycatch monitoring programmes carried out under the EU data collection framework are not targeted towards marine mammal and bird bycatches. Monitoring under the EU council regulation 812/2004 laying down measures concerning incidental catches of cetaceans in fisheries mainly covers trawl gear due to a size limitation in vessels subject to monitoring obligations. Thus, at this point GES cannot be determined.

Relevance of the core indicator

aimed at a general public
1-2 sentences, what is the “role” of the assessed element in the ecosystem (e.g. what role does a seal have in the environment – top predator)?
1-2 sentences, what information of the environment does the parameters in indicator describe/estimate (e.g. what does pregnancy rate of mammals tell the reader about the state of the environment) ?

Thisepressure core indicator follows the number of drowned marine mammals (cetaceans, seals and otters and seals) and diving waterbirds in fishing gears. The populations of these animals are sensitive to added mortality caused by fishing gear, as the animals have characteristics of reproducing slowly Marine mammals are the top predators in the Baltic Sea ecosystem.. Marine mammalTheir population distribution and abundance is closely linked to healthy fish stocks and influenced by many anthropogenic activities. For harbour porpoises, by-catch has been identified as one of the main causes of mortality which may inhibit population recovery.All waterbirds breeding and wintering in the Baltic are characterized by high longevity, low annual reproduction and often a high age of first breeding, making them vulnerable to additive mortality (e.g. Dierschke & Bernotat 2012). As the estimated number of waterbirds drowning in fishing gear represents high proportions of the total population sizes, by-catch is a significant pressure on population trends and demography

This pressure core indicator reflects the sustainability of fishing practices though the effect they have on populations of highly mobile species. The indicator is important to detect intolerable mortality in these key populations. The recent increase in use of anchored gill nets has substantially increased the risk of drowning for the indicator species in the last decades.

In Baltic Sea fisheries, the use of anchored gill nets has substantially increased [LA1]since 1990s (ICES 2007), increasing the conflict between certain fisheries and bird and mammal species as integral parts of the Baltic ecosystem. It has been estimated that a minimum of 300 grey seals, 80 ringed seals and 7–8 harbour seals are captured as by-catch annually in the Baltic Sea (ICES 1995). [SK2]Several studies have shown that the gillnet fishery in the Baltic Sea can in certain places cause high bird mortality, with a rough estimate of 100,000-200,000 waterbirds drowing annually (Zydelis et al. 2009, 2013, Bellebaum et al. 2012). The by-catch problem is of special relevance where gillnet fishery is exercised in the areas with high concentrations of resting, moulting or wintering waterbirds. Fishing mortality may be especially severe for bird species with low reproductive rates and high natural survival rates such as divers and alcids.

Marine mammals are the top predators in the Baltic Sea ecosystem. Their distribution and abundance is closely linked to healthy fish stocks and influenced by many anthropogenic activities. For harbour porpoises, by-catch has been identified as one of the main causes of mortality which may inhibit population recovery. Also for harbour, grey and ringed seals and eurasian otters, drowning in fishing gear is a common cause of death. Thus, the indicator is important to describe the status of the stocks with respect to fishery interaction.

As predators, which are often located at high levels in the food web, waterbirds are an integral part of the Baltic marine ecosystem. A global view on the state of marine birds in the Baltic is given by two indicators observing population sizes of breeding and wintering birds. Since they respond to numerous pressures, many of them owing to anthropogenic impact, key waterbird species can be seen as indicator species. All waterbirds breeding and wintering in the Baltic are characterized by high longevity, low annual reproduction and often a high age of first breeding, making them vulnerable to additive mortality (e.g. Dierschke & Bernotat 2012). As the estimated number of waterbirds drowing in fishing gear represents high proportions of the total population sizes, by-catch has a high impact on population trends and demography. Therefore, the indicator is important to detect intolerable mortality regarding healthy waterbird populations.

Policy relevance of the core indicator

Primary importance / Secondary importance
BSAP
Segment and Objective /

Viable populations of species

Natural Distribution and occurrence of plants and animals

1.1 Species distribution (range, pattern, covered area)
4.1 Productivity of key species or trophic groups (productivity)
MSFD
Descriptors and Criteria / 1.2 Population size (abundance, biomass)
1.3. Population condition (demography, genetic structure)
4.3 Abundance/distribution of key trophic groups and species
Other relevant legislation: EU birds directive, EU habitats directive, Agreement on the Conservation of Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas (ASCOBANS), Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA)

Authors

Sven Koschinski, Volker Dierschke [institutes]

Other recognized contributors: HELCOM SEAL EG[LA3], Lena Avellan (project manager)

Cite this indicator

Koschinski, S. andDierschke, V., [2015].Number of drowned mammals and waterbirds in fishing gear.HELCOM core indicator report.Online. [Date Viewed], [Web link].

Indicator concept

Environmental Target

No Environmental Ttargets has yet been defined for the indicator have not yet been agreed upon for all species and management areas. However, the concept of the Environmental Target has been developed and is based on an ‘acceptable mortality level’ for the indicator species[LA4]. To sustain populations in the long term the mortality in a population must not exceed the birth rate (natality). The indicator species have a slow reproductive rate (K-strategists[LA5]), and thus the acceptable additional mortality stemming from drowning in fishing gear is low.

When setting the Environmental Target values for the indicator species, Where available,otheravailable different types of targets can be used as support, including , defined conservation- targets and removal targets have been defined. Conservation targets are environmental targets focused on the state of a stock or population. Removal targets define either the acceptable anthropogenic mortality (including by-catch) or a maximum by-catch limit. A target for a safe by-catch limit is usually the result of a population dynamic model simulation over a certain time frame within which the target for the stock size is to be reached. In order to set a safe by-catch limit, it has to be agreed upon the time scale of simulations, i.e., the period in which the conservation target should be reached (ICES 2014).

ICES (2013a) concluded that such limits or threshold reference points should take account of uncertainty in existing by-catch estimates into account of, andshould allow current conservation goals to be met, and in order to should enable managers to identify fisheries that require further monitoring, and those where mitigation measures are most urgently required (ICES 2013a).

At present, management objectives for all protected species are unclear at the EU level (ICES 2013a). While broad commitments have been made to ‘Good Environmental Status’ (GES) under the Marine Strategy Framework Directive, and to ‘fFavourable Cconservation Sstatus’ (FCS) under the Habitats Directive, how these objectives may be translated into by-catch limits is as yet unspecified by the European Union. It is to be hoped that the ongoing development of the Marine Strategy Framework Directive will help to address this concern. A therefore preliminary suggestion is that GES will be reached if mammal and waterbird by-catch is below the removal targets and at the same time a trend towards the conservation targets is seen in the population monitoring data.

Alternative methods for setting the Environmental Target

For determining the environmental target that will allow reaching describing GES, a By-catch Risk Approach as outlined in ICES 2013a can be used (ICES 2013a). A By-catch Risk Approach (BRA) was developed initially for cetaceans at the ICES Workshop WKRev812 (ICES 2010) in order to identify areas and fisheries posing the greatest likely conservation threat to by-caught cetacean species. This approach can easily be used for protected species other than cetaceans. The approach splits the population numbers of each protected species into different Management Areas [SK6](MA) and calculates take limits of species by area for any by-catch threshold level used. By using an expected by-catch rate (numbers per day or per unit of catch) multiplied by the total fishing effort, an approximate total number of by-caught animals can be estimated for each fishery and compared with any proposed take limit, such as the 1.7% limit for cetaceans (ASCOBANS, 2000). During WKREV812 this approach enabled fisheries with levels of fishing effort that could pose a potential threat to cetacean species at a regional level to be identified. The approach is summarized below. This approach was adopted in the current Workshop to try to identify fisheries that are most in need of further by-catch monitoring for all protected species. The BRA highlights areas of greatest problem and enables fisheries management decisions.

Another approach is the potential biological removal (PBR) which is used to set a removal target in the US Marine Mammal Protection Act. Rather than using a mean value, as a best estimate for the population size, the lower 20% percentile of the most recent abundance estimate is used as a basis. The conservation goal is the ‘optimum sustainable population’ defined as being at or above the population level that will result in maximum productivity (ICES 2014). The population growth rate and a recovery factor between 0.1 and 1 to introduce an extra level of precaution into the results (usually set to 0.5, in a depleted population 0.1). However, this ’tuning parameter’ could be affected by political horse-trading (Lonergan 2011). The advantage of using the lower 20% percentile of the abundance estimate is that a higher coefficient of variation (synonymous with a higher uncertainty of data) results in lower numbers for the removal target (OrphanidesPalka 2013).

Currently, a project [LA7]is underway to develop a safe by-catch limit using the catch limit algorithm (CLA) based on the IWC's revised management procedure (RMP) for commercial whaling [LA8](ICES 2014). The time span for simulations was set to 100 years [LA9]and the conservation objective was taken from the ASCOBANS targets of 80% of the carrying capacity (whereas the original catch control law of the RMP is ’tuned’ to achieve a population level of 72% of the historic abundance in the long term, 100 years). The difference between CLA and the fixed percentage limit for the Western Baltic Sea population is that CLA accounts for the quality of data (as the PBR does) and further uses a time series of abundance estimates. CLA additionally considers the ratio of the actual abundance estimate and the historic abundance („depletion level“). If this is smaller than 0.54 then the acceptable anthropogenic mortality is set to zero. Whereas the fixed percentage of abundance and PBR approach use only single estimates for bycatch and abundance, CLA fits a population dynamics model to a time-series of abundance estimates and removals data. The advantage is that the accuracy of the CLA approach gets better with increasing data. However, all approaches rely on a suitable monitoring programme as a prerequisite.

CLA is the preferred method in the current discussion since simulations using CLA instead of a fixed percentage of abundance result in shorter recovery time for depleted populations (ICES 2013b, c).

Marine Mammal By-catch. Reference Points. Modelling "safe" by-catch limits such as potential biological removal (PBR) and catch limit algorithm (CLA) for harbour porpoises and various seabird species is necessary for their management in different regions of the Western Baltic, Belt Sea and Kattegat area.

Harbour porpoise[LA10]

Agreed conservation targets for the population size are available for harbour porpoises in the frame of ASCOBANS for the two management units (1) the Kattegat, Belt Sea and Western Baltic population and (2) the Baltic Proper population. ASCOBANS (2002, 2009, 2012) has adopted an interim goal of restoring (and maintaining) the populations of harbour porpoises to at least 80% of their carrying capacity. The ASCOBANS Conservation Plan for the Harbour Porpoise Population in theWestern Baltic, the Belt Sea and the Kattegat (ASCOBANS 2012) states that ASCOBANS has advised that, to be sustainable, the maximum annual anthropogenic induced mortality (including by-catch) for harbour porpoises should not exceed 1.7% of the best estimate of the population size (Resolution No. 3, Incidental Take of Small Cetaceans, Bristol 2000). Scientific analyses indicate that for the critically endangered (2) Baltic Proper population, recovery towards this goal could only be achieved if the by-catch were reduced to two or fewer porpoises per year. This resulted in the objective (i.e. a removal target) of the ASCOBANS Recovery Plan for Baltic Harbour Porpoises (Jastarnia Plan) to reduce the number of by-caught porpoises in the Baltic Proper towards zero (ASCOBANS 2002, 2009).

The International Whaling Commission (IWC) stated that the flag of concern should be raised if the number of small cetaceans captured is greater than 1% of their total population size (Bjørge & Donovan 1995). The 1% limit can also be found in the Resolution No. 3, Incidental Take of Small Cetaceans (Bristol 2000) as an intermediate precautionary objective. The resolution states that where there is significant uncertainty in parameters such as population size or by-catch levels, then ‘unacceptable interaction’ may involve an anthropogenic removal of much less than 1.7 %. To date, the level of by-catch is of unknown magnitude for both management units. Thus, from this perspective the removal target should be less than 1% (Czybulka et al. in prep). For the Baltic Proper population, even the size of the population is unknown. In December 2014, the result of the SAMBAH project assessing the abundance in the Baltic Proper by means of 300 acoustic data loggers is expected. The estimated size of the Western Baltic Sea population is 18,495 animals (CV = 0.27, 95% CI: 10,892-31,406) (Sveegaard et al. 2013).

The Oother above listed approaches, than setting a fixed percentage of abundance taking the uncertainty of data into account, have already been developed. Using these other methods and should replace the abovementioned targets for the different species and management units should be replaced as soon as simulations are available[LA11].

One such approach is the potential biological removal (PBR) which is a removal target by the US Marine Mammal Protection Act. Rather than using a mean value as best estimate for the population size, the lower 20% percentile of the most recent abundance estimate is used as a basis. The conservation goal is the "optimum sustainable population" defined as being at or above the population level that will result in maximum productivity (ICES 2014). The population growth rate and a recovery factor between 0.1 and 1 to introduce an extra level of precaution into the results (usually set to 0.5, in a depleted population 0.1). However, this "tuning parameter" could be affected by political horse-trading (Lonergan 2011). The advantage of using the lower 20% percentile of the abundance estimate is that a higher coefficient of variation (synonymous with a higher uncertainty of data) results in lower numbers for the removal target (Orphanides & Palka 2013).