Harbour porpoise in the Baltic region and North Sea

There are three populations of harbour porpoise (Phocoena phocoena) in the Baltic region (Fig. 2): 1) the North Sea population, with a management range from the northern Kattegat, through Skagerrak to the entire North Sea, 2) the Belt Sea population in the western Baltic Sea, Belt Sea, the Sound and southern Kattegat, and 3) the Baltic Proper population in the inner Baltic Sea (Owen et al. 2022).

<figure><img src="image_185.png" /><figcaption>**Figure 2.** Map showing the approximate distributions of harbor porpoise populations in the Baltic Sea Region From Carlén et al. (2021).</figcaption></figure>

The Baltic proper population is listed by the International Union for Conservation of Nature (IUCN) and the Baltic Marine Environment Protection Commission (HELCOM) as critically endangered. Its abundance was estimated in a two-year acoustic survey in 2011–2013, resulting in an estimate of 497 animals (95% CI 80–1091; CV=0.42) (ICES 2020b). While pollution and disturbance through underwater noise may be contributing to the population failing to recover, bycatch is the one acute threat causing direct mortalities in significant numbers (ICES 2020b). For this population, conventional PBR was applied but using Fr=0.1 (instead of the default value of 0.5) given its critical conservation status (Wade 1998). This led to a maximum of 0.7 animals bycaught per year (Table 3).

For the Belt Sea population, we considered the latest abundance estimate (Lacey et al. 2022) but adapted to cover the Kattegat (ICES area IIIa21), the Sound (ICES area 266 IIIb23), and the Belt Seas (ICES area IIIc22), resulting in 16,678 individuals (CV=0.2). For this population, conventional PBR and mPBR were applied but with two levels of assumptions: in the first, a classical value of 0.5 was used as Fr for PBR and 0.15 for mPBR following Genu et al. (2021). This led to 141 and 42
individuals respectively. The second estimate incorporated knowledge, as planned in the PBR and mPBR robustness scenarios, on the precision of the abundance and bycatch rate estimates. Under these assumptions, 1.0 was used as Fr for PBR and 0.35 for mPBR (Kindt-Larsen et al. 2023). This led to 282 and 99 individuals, respectively.
In the North Sea, the overall abundance of harbour porpoise was estimated to be 345,000 individuals (95% CI 246,526-495,752; CV= 0.18) based on SCANS-III survey in 2016 (Hammond et al. 2017). For this population, Removals Limit Algorithm (RLA) was calculated, which provided a threshold of 1622 individuals (ICES 2021b) (Table 3).

This approach is considered a more sophisticated management procedure than PBR (Palialexis et al. 2021) and requires both bycatch and abundance estimates. From these data, it estimates, through a population dynamic model (usually fit in Bayesian framework), two key parameters: current depletion Dt, and population growth rate, r (Hammond et al. 2019). Once these two parameters have been estimated, the anthropogenic mortality limit is computed as:

$$ \text{Antropogenic mortality limit} = N \times r \times \max(0, Dt - IPL) \quad (2) $$

where N is the best available abundance estimate and IPL is the internal protection level set to 0.54 (i.e. 54% of carrying capacity K). If the estimated depletion level of the population is below the IPL, then the bycatch limit is set to 0.

<table><caption>**Table 3.** Bycatch thresholds estimated through different methods. Parameters needed to estimate the thresholds are also included as well as the organisms and/or studies that apply them (note that RLA estimation does not follow PBR procedure).</caption><thead><tr><th>Population</th><th>Method</th><th>N</th><th>Nmin</th><th>Rmax</th><th>Fr</th><th>Threshold</th><th>Organization</th><th>Reference</th><th></th></tr></thead><tbody><tr><td></td><td>Baltic proper population</td><td>PBR</td><td>497</td><td>360</td><td>0.04</td><td>0.1</td><td>0.7</td><td>ICES</td><td>ICES (2020b)</td></tr><tr><td rowspan="2">Balt Sea population</td><td>PBR</td><td>16678</td><td>14116</td><td>0.04</td><td>0.5-1</td><td>141-282</td><td rowspan="2">--</td><td rowspan="2">Kindt-Larsen et al. (2023)</td><td rowspan="2"></td></tr><tr><td>mPBR</td><td></td><td></td><td></td><td>0.15-0.35</td><td>42-99</td></tr><tr><td>North Sea population</td><td>RLA</td><td>--</td><td>--</td><td>--</td><td>--</td><td>1622</td><td>OSPAR</td><td>ICES (2021b)</td><td></td></tr></tbody></table>

According to the data presented in the latest Working Group on Bycatch of Protected Species for the 2017-2021 period (WGBYC; ICES 2022d), harbour porpoise is caught in the Baltic and North Sea in bottom otter trawls (OTB), gillnets (GNS) and trammel nets (GTR) and Danish seines (SDN) (Table 4).

Bycatch rates for these metiers were estimated using the number of animals recorded bycaught divided by days at sea observed. The number of bycaught animals and days at sea observed were aggregated by ICES Ecoregion and Métier Level 4 (rates based on less than 50 days at sea
observed should be taken with caution). Confidence intervals around the bycatch rates were
estimated assuming a binomial distribution (ICES 2022d).
<table><caption>**Table 4.** Harbour porpoise bycatch rates (no. of animals per day) and 95% confidence intervals around the rates provided for the Baltic Sea and Greater North Sea by métier level 4 over the 2017-2021 period. Days at Sea (Das) refers to observed effort while coverage (not always available) refers to the % of days observed respect to total effort.</caption><thead><tr><th>Region</th><th>Metier</th><th>DaS</th><th>Coverage (%)</th><th>No. of animals</th><th>Rate</th><th>CI5-CI95</th></tr></thead><tbody><tr><td rowspan="2">Baltic Sea</td><td>GNS</td><td>1116</td><td>--</td><td>30</td><td>0.026</td><td>0.018-0.034</td></tr><tr><td>GTR</td><td>105</td><td>--</td><td>1</td><td>0.009</td><td>0-0.028</td></tr><tr><td rowspan="4">Greater North Sea</td><td>GNS</td><td>8170</td><td>--</td><td>416</td><td>0.050</td><td>0.046-0.055</td></tr><tr><td>GTR</td><td>641</td><td>--</td><td>11</td><td>0.017</td><td>0.009-0.026</td></tr><tr><td>SDN</td><td>107</td><td>--</td><td>1</td><td>0.009</td><td>0-0.028</td></tr><tr><td>OTB</td><td>4194</td><td>--</td><td>1</td><td>0.0002</td><td>0-0.0007</td></tr></tbody></table>

Whilst the above thresholds are estimated for three porpoise populations, bycatch rates can only be found for two ecoregions. Data presented in previous reports, however, suggest that for the Baltic proper population, the bycatch estimated for 2017 (7 animals) and for the years 2000-2012 (3 animals per year on average) exceed the threshold of 0.7 animals (ICES 2020b).

For the Belts Sea, the average annual bycatch for 2020 was predicted to be 938 (249-3676) porpoises when no pinger was used, and 861 (238-31968) when pingers were used. In both cases, the predicted total bycatch amount was above the sustainable bycatch limits or thresholds (Kindt-Larsen et al. 2023).

For the north Sea, the total number porpoises that were bycaught in 2020 was estimated to be 5929 (95% CI 3176-10739) when including all countries (but believed to be heavily skewed) and 1627 (95% CI 922-3325) when not including the unrepresentative data (ICES 2021b). The lower estimate of bycatch estimated in the North Sea, 1627 individuals (95% CI 921-3325), only slightly exceeds the threshold while the higher estimate, 5929 individuals (95% CI 3176-10739), exceeds the threshold significantly.
## Harbour porpoise in Irish and adjacent waters

Bycatch rates for harbour porpoise for the Celtic Seas Ecoregion can also be found in the latest WGBYC report (ICES 2022d). However, the recent report from the ICES Workshop on Estimation of Mortality of Marine Mammals Due to Bycatch (WKMOMA) gives a more detailed breakdown by OSPAR assessment unit and also gives the corresponding mPBR threshold estimates for those areas (which make up most of Celtic seas Ecoregion) (Fig. 3, Table 5)(ICES 2021b).

<figure><img src="image_186.png" /><figcaption>**Figure 3:** OSPAR assessment units for bycatch of harbour porpoise. From WKMOMA (ICES 2021b).</figcaption></figure>

<table><caption>**Table 5.** Reported monitoring effort (days at sea, DaS) and bycatch rate (no. of animals per day) for harbour porpoise from 2005 - 2021, as well as the OSPAR mPBR from WKMOMA. Metiers reported are those where bycatch was observed.</caption><thead><tr><th>Assessment area</th><th>Metier</th><th>DaS</th><th>No. of animals</th><th>Rate</th><th>OSPAR mPBR threshold</th></tr></thead><tbody><tr><td rowspan="6">Celtic seas</td><td>GND</td><td>332.10</td><td>9</td><td>0.03</td><td rowspan="6">43</td></tr><tr><td>GNS</td><td>5271.35</td><td>94</td><td>0.02</td></tr><tr><td>GTR</td><td>4418.67</td><td>83</td><td>0.02</td></tr><tr><td>OTB</td><td>11252.86</td><td>5</td><td>0.0004</td></tr><tr><td>OTT</td><td>6835.26</td><td>3</td><td>0.0004</td></tr><tr><td>PTM</td><td>1413.05</td><td>4</td><td>0.003</td></tr><tr><td>Irish Seas</td><td>GNS</td><td>58.7</td><td>1</td><td>0.02</td><td>34</td></tr><tr><td rowspan="3">West of Scotland and Ireland</td><td>GNS</td><td>641.33</td><td>2</td><td>0.003</td><td rowspan="3">78</td></tr><tr><td>GTR</td><td>24</td><td>2</td><td>0.08</td></tr><tr><td>OTB</td><td>7537.3</td><td>1</td><td>0.0001</td></tr></tbody></table>

Readers should be aware that total bycatch estimates (no. of animals) in a given year may be much higher than those in the table above. Bycatch numbers in the table are only those
associated with the observed DaS. In the WKMOMA report, bycatch estimates for 2020 are reported and compared to the mPBR. For example, estimated bycatch of harbour porpoises in the Celtic Seas assessment unit for 2020 was 738 (284-2240) animals. The mPBR set by OSPAR for that assessment unit was 43 animals and estimated bycatch is therefore much higher than the threshold.
## Pinnipeds

### Grey seal in the North Sea

The grey seal *Halichoerus grypus* has a cold temperate to sub-Arctic distribution in North Atlantic waters over the continental shelf (Hall & Russell 2018). In the northeast Atlantic population is concentrated around the UK and Ireland but is also found around Iceland, the Faroe Islands, and along the European mainland coast from the Kola Peninsula south to southern Norway, and from Denmark to Brittany in France. The Baltic Sea subpopulation is confined to the Baltic Sea (Hall & Russell 2018).

<figure><img src="image_187.png" /><figcaption>**Figure 4:** OSPAR assessment units for grey seal. From WKMOMA (ICES 2021b).</figcaption></figure>

For the grey seal several assessment units have been defined (Fig. 4); however, anthropogenic removal thresholds could only be estimated for the Greater North Sea. In this case, conventional PBR was applied, but setting Rmax= 0.12, the default value for pinnipeds (Wade 1998). Unlike with common dolphin and harbor porpoise, Fr=1 was used because grey seals in the Greater North Sea are increasing throughout the region (Bowen 2016). A Fr of 1 has also been used in the UK for setting PBR limits (Thompson et al. 2021) and is justified when populations are well studied and biases in population estimates are negligible or when populations are known to be at optimum level or increasing.

Grey seals are not monitored in a consistent way throughout the North Sea which means deriving Nmin based on the 20th percentile of the best abundance estimate was not feasible. The following approach to calculate Nmin was therefore taken, using a combination of count data:

1. August survey counts scaled to population size from the UK (2016-2019)

2. Moult counts from France, Netherlands and Wadden Sea (2019/2020)
Counts from Belgium, Sweden and Norway were not included in this example; but there are very few seals within the OSPAR region II in these countries. This approach resulted in an Nmin of 126,956 animals (ICES, *in prep*). When applying these values in equation 1, an anthropogenic removal limit of 7,617 individuals was obtained (Table 6).

<table><caption>**Table 6.** Bycatch thresholds estimated through PBR approach. Parameters needed to estimate the thresholds are also included as well as the organisms and/or the studies that apply them.</caption><thead><tr><th>Species</th><th>Method</th><th>N</th><th>Nmin</th><th>Rmax</th><th>Fr</th><th>Threshold</th><th>Organisation</th><th>Reference</th></tr></thead><tbody><tr><td>North Sea</td><td>PBR</td><td>---</td><td>126,956</td><td>0.12</td><td>1</td><td>7617</td><td>OSPAR</td><td>ICES (2021b)</td></tr></tbody></table>

*Total population estimate was not provided.*

According to the data presented in the latest Working Group on Bycatch of Protected Species for the 2017-2021 period (WGBYC; ICES 2022d), grey seal in the greater North Sea, is caught, although in different rates, in gillnets (GNS) and trammel nets (GTR), midwater otter trawls (OTM), bottom otter trawls (OTB) and beam trawls (TBB) (Table 7).

Bycatch rates for these metiers were estimated using the number of animals recorded bycaught divided by days at sea observed. The number of bycaught animals and days at sea observed were aggregated by ICES Ecoregion and Métier Level 4 (rates based on less than 50 days at sea observed should be taken with caution). Confidence intervals around the bycatch rates were estimated assuming a binomial distribution (ICES 2022d).

<table><caption>**Table 7.** Grey seal bycatch rates (no. of animals per day) and 95% confidence intervals around the rates provided for the North Sea by métier level 4 over the 2017-2021 period. Days at Sea (Das) refers to observed effort while coverage (not always available) refers to the % of days observed respect to total effort.</caption><thead><tr><th>Ecoregion</th><th>Metier</th><th>DaS</th><th>Coverage (%)</th><th>No. of animals</th><th>Rate</th><th>CI5-CI95</th></tr></thead><tbody><tr><td rowspan="5">North Sea</td><td>GNS</td><td>8170</td><td>--</td><td>11</td><td>0.0013</td><td>0.0007-0.002</td></tr><tr><td>GTR</td><td>641</td><td>--</td><td>8</td><td>0.012</td><td>0.006-0.02</td></tr><tr><td>TBB</td><td>1526</td><td>--</td><td>1</td><td>0.00065</td><td>0-0.0019</td></tr><tr><td>OTB</td><td>4194</td><td>--</td><td>1</td><td>0.00023</td><td>0-0.00071</td></tr><tr><td>OTM</td><td>694</td><td>--</td><td>23</td><td>0.033</td><td>0.021-0.044</td></tr></tbody></table>

Note that those bycatch numbers are only associated with the observed DaS. The overall bycatch estimates for grey seal in the Great North Sea assessment unit was 2229 individuals (95% CI 1598-3199) based on bycatch events from 2015-2020 and raised with effort data from 2020 (ICES 2021b).
This estimate is considerably lower than the PBR threshold set by OSPAR of 7617 grey seals in the
Great North Sea.
# Seabirds

## Northern fulmar and Northern gannet in Irish waters

Population estimates of Irish colonies of Northern fulmar *Fulmarus glacialis* and Northern gannet *Morus bassanus* were taken from a reasonably recent National Parks and Wildlife Service (NPWS) report (Cummins et al. 2019). Surveys were conducted between 2015-2018 for fulmar and 2013-2014 for gannet. It should be noted that there have been more recent more recent surveys and results of these are expected to be published later this year. Other sources of seabird population estimates were also considered, primarily those from the ObSERVE report. ObSERVE survey estimates are for offshore seabirds so are likely to be underestimates of population size, however these estimates may be useful in the future if looking at a more specific area (i.e. the specific area coverage of the EWE model) (Rogan et al. 2018).

Life history parameters (adult survival/mortality and age at first breeding) for both species were obtained from two different sources to account for uncertainty in the estimates. The first source was "Birds of the World" by the Cornell Lab of Ornithology (Mallory et al. 2020, Mowbray 2020), with the exception of fulmar age at first breeding (Robinson 2005). The second source was a list of seabird life history parameters collated by (Bird et al. 2020).

The BLT is the recommended method from BirdLife International for seabirds and is theoretically the most simple of the two methodologies, where the BLT is 1% of an adult population's annual mortality, N is the number of the population and m is the annual mortality of adults in the population (BirdLife International 2019).

$$BLT = \frac{Nm}{100} \qquad (3)$$

This method is inherently very conservative by design. In their pilot assessment OSPAR propose applying this method to species on the "OSPAR List of Threatened and/or Declining Species and Habitats" (OSPAR Agreement 2008-06) and state that the method is an approximation of zero bycatch, which acknowledges that there will still be a small number of incidental mortalities (Dierschke 2022). Birdlife International justify this approach in a similar context, whilst also stating that threshold values should only be used to determine "Good Environmental Status" and not as a limit to trigger management of the impact of fisheries (BirdLife International 2019).

<caption>**Table 8.** Population estimates, adult mortality estimates and BirdLife International Threshold (BLT) range for two seabird species in Ireland. The BLT range (no. of birds, rounded down to the nearest integer) was calculated using the two differing adult mortality values for each species.</caption>

PBR is a method that has been commonly used for marine mammals and in many cases seabirds

<table><thead><tr><th>SPECIES</th><th>POPULATION ESTIMATE</th><th>M (CORNELL)</th><th>M (BIRD ET AL. 2020)</th><th>BLT</th></tr></thead><tbody><tr><td>FULMAR</td><td>65798</td><td>0.012</td><td>0.03</td><td>7 - 19</td></tr><tr><td>GANNET</td><td>95892</td><td>0.08</td><td>0.06</td><td>57 - 76</td></tr></tbody></table>

as well. In the case of seabirds, previous studies have defined Nmin as the lower boundary of the breeding population estimate within a 60% confidence interval (Dillingham & Fletcher 2008,
Marchowski 2022). In order to estimate Nmin a coefficient of variation is needed for population estimates. These were not available from the NPWS report, however there were brief summaries on the confidence in the estimates (medium for fulmar and high for gannet) within the report and CVs (0.3 for fulmar and 0.1 for gannet) were decided upon based on this.

By changing the level of f used in the PBR formula the user can in theory determine whether to maintain a population at or above the maximum net productivity level or reduce the time to recovery, with 0.1 giving the most conservative threshold (Wade 1998). For a useful summary of factors to take into account when selecting an f value readers should see Dillingham and Fletcher (2008).

Obtaining a value for Rmax can be problematic, however using the relationship with population growth rate (λmax) a value be estimated. Population growth rate (λmax[08,10,16]).

$$ \lambda_{max} = e^{\left[ \left( \alpha + \frac{s}{\lambda_{max} - s} \right)^{-1} \right]} \quad (4) $$

$$ R_{max} = |\lambda_{max} - 1| \quad (5) $$

Equation 4 can be solved numerically to give λmax and in turn Rmax (equation 5)

<table><caption>**Table 9.** Population estimates (N), lower boundary of the breeding population estimate within a 60% confidence interval (Nmin), adult survival (s), age at first breeding (α) and maximum net recruitment rate (Rmax) for Irish colonies of fulmar and gannet. Rmax values were calculated using equations 5 and 6 with s and α values.</caption><thead><tr><th rowspan="2">Species</th><th rowspan="2"></th><th colspan="3">Cornell</th><th colspan="3">Bird et al. (2020)</th></tr><tr><th></th><th></th><th></th><th></th><th></th><th></th></tr></thead><tbody><tr><td>Fulmar</td><td>65798</td><td>51419</td><td>0.986</td><td>9</td><td>0.035</td><td>0.97</td><td>8.5</td><td>0.049</td></tr><tr><td>Gannet</td><td>95892</td><td>88185</td><td>0.92</td><td>5.5</td><td>0.098</td><td>0.94</td><td>4</td><td>0.111</td></tr></tbody></table>

<table><caption>**Table 10.** Potential Biological Removal (PBR) threshold values for two seabird species in Ireland. PBRs were estimated from two different sources of life history parameters and five levels of recovery factor (f).</caption><thead><tr><th rowspan="2">Species</th><th rowspan="2">f</th><th colspan="2">PBR</th></tr><tr><th>Cornell</th><th>Bird et al. (2020)</th></tr></thead><tbody><tr><td rowspan="5">Fulmar</td><td>0.1</td><td>90</td><td>127</td></tr><tr><td>0.2</td><td>179</td><td>254</td></tr><tr><td>0.3</td><td>269</td><td>382</td></tr><tr><td>0.4</td><td>359</td><td>509</td></tr><tr><td>0.5</td><td>448</td><td>636</td></tr></tbody></table>
<table><tr><td></td><td>0.1</td><td>434</td><td>490</td></tr><tr><td></td><td>0.2</td><td>867</td><td>979</td></tr><tr><td></td><td>0.3</td><td>1301</td><td>1469</td></tr><tr><td>Gannet</td><td>0.4</td><td>1735</td><td>1959</td></tr><tr><td></td><td>0.5</td><td>2169</td><td>2449</td></tr></table>

Whilst the above PBR thresholds are estimated for the Irish breeding population of fulmar and gannet, bycatch rates for these two species of seabird can only be found for the wider Celtic Seas ecoregion and not solely Irish waters or the specific area the Celtic Sea EWE model covers (ICES 2022d).

**Table 11:** Bycatch rates (no. of animals per day), 95% confidence intervals, observed days at sea (DaS) and observed number of animals as bycatch for each relevant metier for northern fulmar and northern gannet in the Celtic Seas Ecoregion as collated by in the WGBYC 2022 report (ICES, 2022). DaS are round to 2 d.p., rate and C.I.s are to 3 s.f.

<table><thead><tr><th>Species</th><th>Metier</th><th>DaS</th><th>No. of animals</th><th>Rate</th><th>C.I.5</th><th>C.I.95</th></tr></thead><tbody><tr><td rowspan="3">Fulmar</td><td>LLS</td><td>179.75</td><td>12</td><td>0.0668</td><td>0.0389</td><td>0.100</td></tr><tr><td>LLS</td><td>179.75</td><td>14</td><td>0.0779</td><td>0.0445</td><td>0.111</td></tr><tr><td>PTB</td><td>29.47</td><td>2</td><td>0.0678</td><td>0</td><td>0.169</td></tr><tr><td rowspan="3">Gannet</td><td>OTB</td><td>3848.74</td><td>17</td><td>0.00442</td><td>0.00286</td><td>0.00625</td></tr><tr><td>PTM</td><td>332.53</td><td>1</td><td>0.00301</td><td>0</td><td>0.00902</td></tr><tr><td>TBB</td><td>1091.60</td><td>2</td><td>0.00183</td><td>0</td><td>0.00458</td></tr></tbody></table>
## Balearic shearwater in the Mediterranean Sea and Western Waters

The Balearic shearwater *Puffinus mauretanicus* is the most threatened seabird in Europe and listed as “Critically Endangered” (Birdlife International 2023). The species breeds exclusively at the Balearic Islands, but migrates to the Northeast Atlantic during the non-breeding season (late spring-early summer) presumably to exploit highly rich productive areas (Pérez-Roda et al. 2017).

For the PBR calculation, we used, as with cetaceans, the 20th percentile of the distribution of population size following Genovart et al. (2016). The population size was estimated based on coastal migrations counts (Arroyo et al. 2016) and ranged between 23780 and 26535 individuals (minimum value was taken here). Rmax = 0.101 (λmax-1) was used and Fr=0.1, conservative value typical for endangered species (Genovart et al. 2016). As a result, a PBR of 101 individuals was obtained (Table 12).

<table><caption>**Table 12.** Bycatch thresholds estimated through PBR approach. Parameters needed to estimate the thresholds are also included as well as the organisms and/or studies that apply them.</caption><thead><tr><th>Species</th><th>Method</th><th>N</th><th>Nmin</th><th>Rmax</th><th>Fr</th><th>Threshold</th><th>Organization</th><th>Reference</th></tr></thead><tbody><tr><td>Balearic shearwater</td><td>PBR</td><td>23780</td><td>19965</td><td>0.101</td><td>0.1</td><td>101</td><td>--</td><td>Genovart et al. (2016)</td></tr></tbody></table>

In the Mediterranean, the species mainly interacts with pelagic longline (LLD) (Genovart et al. 2016); in the Atlantic, according to the data presented in the latest Working Group on Bycatch of Protected Species for the 2017-2021 period (WGBYC; ICES 2022d), the species is also caught in bottom otter trawls (OTB), gillnets (GNS), trammel nets (GTR) and set longlines (LLS) (Table 13).

Bycatch rates for these metiers were estimated using the number of animals recorded bycaught divided by days at sea observed. The number of bycaught animals and days at sea observed were aggregated by ICES Ecoregion and métier Level 4. Confidence intervals around the bycatch rates were estimated assuming a Poisson distribution using the function qpois in R. Poisson distribution was selected rather than binomial, after an analysis conducted in 2020 investigating which error distribution was the most suitable for data in the WGBYC database.

<table><caption>**Table 13.** Balearic shearwater bycatch rates (no. of animals per day) and 95% confidence intervals around the rates provided by métier level 4 for 2017-2021 period (pooled). Days at Sea (Das) refers to observed effort while coverage (not always available) refers to the % of days observed respect to total effort.</caption><thead><tr><th>Region</th><th>Metier</th><th>DaS</th><th>Coverage</th><th>No. of animals</th><th>Rate</th><th>CI5- CI95</th></tr></thead><tbody><tr><td></td><td>GTR</td><td>1730</td><td>--</td><td>5</td><td>0.002</td><td>0.001-0.005</td></tr></tbody></table>
SEAwise - WP4.2 – Thresholds and bycatch rates for PET species

<table><tbody><tr><td rowspan="3">Bay of Biscay and Iberian Coast</td><td>GNS</td><td>2875</td><td>--</td><td>4</td><td>0.001</td><td>0.0003-0.002</td></tr><tr><td>OTB</td><td>1637</td><td>--</td><td>2</td><td>0.001</td><td>0-0.003</td></tr><tr><td>LLS</td><td>364</td><td>--</td><td>1</td><td>0.002</td><td>0-0.008</td></tr><tr><td>Western Mediterranean Sea</td><td>LLD</td><td>2110</td><td>--</td><td>33</td><td>0.033</td><td>0.021-0.046</td></tr></tbody></table>

Current WKBYC bycatch data, and the fact that bycatch in artisanal fisheries is rarely monitored, do not allow inferring total bycatch numbers from extrapolations of these data (ICES 2022d). However, the estimated bycatch rate of about half of the mortality detected in Genovart et al. (2016) confirms that current fishery impact is unsustainable and that should be reduced urgently to avoid extinction.
# Reptiles

## Loggerhead turtle in the Mediterranean Sea

The loggerhead turtle *Caretta caretta* is the most abundant sea turtle species in the Mediterranean. It frequents the entire marine area of the Mediterranean, with high occurrence reported in the oceanic zones of the westernmost part of the basin (from the Alboran Sea to the Balearic Islands), the Strait of Sicily, and the Ionian Sea (Casale & Margaritoulis 2010). Its Mediterranean population is recognized as regional management unit, and it is subject to several anthropogenic threats, including incidental capture in fishing gear (Casale 2011), despite being listed as Least Concern by the IUCN.

The size and demographic structure of sea turtle populations are commonly unknown, and until recently, only the number of adult females nesting annually in the Mediterranean had been estimated (Broderick et al. 2002). Under such circumstances, Curtis and Moore (2013) developed the Reproductive Value Loss Limit (RVLL), a maximum bycatch estimation approach which uses reproductive value equivalents in place of the number of individuals.

In the last years, however, new attempts to estimate the population size of sea turtles have arisen, enabling the application of PBR. Casale and Heppell (2016), for example, estimated the population of the Mediterranean loggerhead turtle through a stationary age distribution model. By assuming a sexual maturity age of 21 years, they estimated a population of 1,197,087 (95% CI: 805,658 -1,732,675) individuals for the whole basin. In 2022, DiMatteo et al. (2022) applied species distribution models to the data collected between 2003 and 2018 on aerial and ship surveys, estimating a total abundance of 1,201,845 (CV=0.22; 95% CI: 838,864-1,548,280) turtles.

For the PBR calculation, we have applied the latest abundance estimate (DiMatteo et al. 2022), as it also provides a confidence interval value. As recovery factor, we will assume the default value, which is used when the species is threatened or has unknown status. For the productivity rate we will use the same as in Casale and Heppell (2016) (Table 14).

<table><caption>**Table 14.** Bycatch thresholds estimated through PBR approach. Parameters needed to estimate the thresholds are also included as well as the organisms/studies that apply them.</caption><thead><tr><th>Species</th><th>Method</th><th>N</th><th>Nmin</th><th>Rmax</th><th>Fr</th><th>Threshold</th><th>Organization/<br>Reference</th></tr></thead><tbody><tr><td>Loggerhead turtle</td><td>PBR</td><td>1,201,845</td><td>1,003,541</td><td>0.064</td><td>0.5</td><td>16057</td><td>Adapted<br>from<br>Casale<br>and<br>Heppell<br>(2016)</td></tr></tbody></table>

According to the data presented in the latest Working Group on Bycatch of Protected Species for the 2017-2021 period (WGBYC; ICES 2022d), loggerhead turtle in the Mediterranean is caught in longlines (LLD), midwater pair trawls (PTM), bottom otter trawls (OTB), otter twin trawls (OTT), trammel nets (GTR) and purse seiners (PS) (Table 15).
Bycatch rates for these metiers were estimated using the number of animals recorded bycaught divided by days at sea observed. The number of bycaught animals and days at sea observed were aggregated by ICES Ecoregion and Métier Level 4 (rates based on less than 50 days at sea observed should be taken with caution). Confidence intervals around the bycatch rates were estimated assuming a Poisson distribution using the function qpois in R. Poisson distribution was selected rather than binomial, after an analysis conducted in 2020 investigating which error distribution was the most suitable for data in the WGBYC database.
<table><caption>**Table 15.** Loggerhead turtle bycatch rates (no. of animals per day) and 95% confidence intervals around the rates provided for the Mediterranean basin by métier level 4 for 2017-2021 period (pooled). Days at Sea (Das) refers to observed effort while coverage (not always available) refers to the % of days observed respect to total effort.</caption><thead><tr><th>Region</th><th>Metier</th><th>Das</th><th>Total effort in days</th><th>Coverage (%)</th><th>No. of animals</th><th>rate</th><th>CI5-CI95</th></tr></thead><tbody><tr><td>Adriatic Sea</td><td>LLD</td><td>167</td><td>2389</td><td>6.9</td><td>15</td><td>0.089</td><td>0.053-0.131</td></tr><tr><td>Western Mediterranean</td><td>LLD</td><td>2110</td><td>24679</td><td>8.5</td><td>46</td><td>0.042</td><td>0.029-0.057</td></tr><tr><td>Adriatic Sea</td><td>PTM</td><td>988</td><td>10532</td><td>9.3</td><td>67</td><td>0.067</td><td>0.054-0.081</td></tr><tr><td>Adriatic Sea</td><td>OTB</td><td>464</td><td>130920</td><td>0.3</td><td>20</td><td>0.043</td><td>0.028-0.060</td></tr><tr><td>Aegean-Levantine Sea</td><td>OTB</td><td>544</td><td>--</td><td>--</td><td>3</td><td>0.005</td><td>0.001-0.011</td></tr><tr><td>Western Mediterranean</td><td>OTB</td><td>2842</td><td>301564</td><td>0.9</td><td>3</td><td>0.001</td><td>0.0003-0.002</td></tr><tr><td>Western Mediterranean</td><td>OTT</td><td>455</td><td>130773</td><td>0.3</td><td>2</td><td>0.004</td><td>0-0.010</td></tr><tr><td>Aegean-Levantine Sea</td><td>GTR</td><td>1392</td><td>--</td><td>--</td><td>1</td><td>0.0007</td><td>0-0.002</td></tr><tr><td>Adriatic Sea</td><td>PS</td><td>362</td><td>23601</td><td>1.5</td><td>21</td><td>0.058</td><td>0.038-0.080</td></tr><tr><td>Ionian Sea and the Central</td><td>PS</td><td>35</td><td>--</td><td>--</td><td>0</td><td>0</td><td>0</td></tr></tbody></table>

Note that those bycatch numbers are only associated with the observed Das. In The Adriatic Sea data from four métiers (PTM, LLD, PS, OTB) were available with reported bycatch of loggerhead turtles but only two of those métiers (LLD and PS) were suitable for calculations of bycatch estimates. The total annual estimate of bycatch in drifting longlines (LLD) was between 129-315 turtles, while the estimate in purse seines (PS) was between 913-1891 turtles. Therefore, for the Adriatic Sea, the total minimum bycatch for LLD and PS only is between 1042 and 2206 turtles annually (although high bycatch rates for loggerhead turtles are known to occur in OTB and PTM)(ICES 2022d).

In the western Mediterranean three métiers (OTB, LLD, OTT) reported bycatch of loggerhead sea turtles but only two of those métiers (OTB and OTT) were suitable for calculations of bycatch estimates. The estimate for otter bottom trawl (OTB) was between 106-637 turtles annually, while the estimate in otter twin (or multi-rig) trawla (OTT) was between 0 and 1437 turtles. In the Western Mediterranean, therefore, the total minimum bycatch estimate is between 106 and 2074 turtles annually(ICES 2022d). By summing both estimates, the total amount of bycaught turtles would be between 1148-4280.
# Fish

## Spurdog in Northeast Atlantic and adjacent waters

The Spurdog *Squalus acanthias* has a cosmopolitan distribution in boreal and temperate waters of the Atlantic and Pacific Oceans. In the Northeast Atlantic, spurdog is distributed widely in shelf seas and occurs from Iceland and the Barents Sea southwards to Northwest Africa and the Mediterranean Sea, although it is most common north of the Bay of Biscay (Ebert et al. 2013).

They are a slow-growing, late-maturing species, and have low fecundity (Hammond & Ellis 2004). These K-strategy life history traits, along with this species' high susceptibility to fishing gear make the spurdog highly vulnerable to overfishing (McCully et al. 2013). This vulnerability has been demonstrated in the Northeast Atlantic, where spurdog biomass has declined by more than 90% due to commercial fishing (Hammond & Ellis 2004). This magnitude of depletion was used to list it as "Critically Engandered" according to the Red List criteria of the International Union for Conservation of Nature (IUCN), although current estimates of depletion suggest an IUCN listing of "Endangered" (De Oliveira et al. 2013).

Spatial management of the remaining NE Atlantic population has been hampered because spurdog is generally considered a highly mobile species, and this population is thought to be a single, large, stock unit, undertaking large-scale seasonal movements (Vince 1991). In 2021 the stock of the Northeast Atlantic and adjacent waters (subareas 1-10,12 and 14) was benchmarked (ICES 2021a). There was a substantial improvement in data available for the stock assessment and improved catch information since 2005 (ICES 2022b).

<table><caption>**Table 16.** Maximum catches of spurdog that should not be exceeded for 2023 and 2024 when the MSY approach is applied, as well as the organization/studies that apply or recommend this approach.</caption><thead><tr><th>SPECIES</th><th>METHOD</th><th>YEAR</th><th>THRESHOLD</th><th>ORGANIZATION</th><th>REFERENCE</th></tr></thead><tbody><tr><td rowspan="2">SPURDOG</td><td>MSY</td><td>2023</td><td>17353</td><td rowspan="2">ICES</td><td rowspan="2">ICES (2022b)</td></tr><tr><td>MSY</td><td>2024</td><td>17855</td></tr></tbody></table>

ICES advice suggest that when the MSY approach is applied, catches in 2023 and 2024 should be no more than 17 353 tonnes and 17 855 tonnes, respectively (Table 16) (ICES 2022b). In 2021, 1178 tonnes of spurdog were caught (Table 17); 639 tonnes were discards, while 539 tonnes were landings, coming from nets mainly (ICES 2022b). Currently, fishing pressure on the stock is below $HR_{MSY}$, and spawning-stock size is above MSY $B_{trigger}$, $B_{pa}$, and $B_{lim}$ (ICES 2022b).

<table><caption>**Table 17.** Spurdog catch distribution by fleet in 2021 as estimated by ICES for the Northeast Atlantic</caption><thead><tr><th>Total catch</th><th colspan="4">Landings</th><th>Discards</th></tr></thead><tbody><tr><td rowspan="2">1178 tonnes</td><td>Nets</td><td>Bottom trawl</td><td>Hooks and lines</td><td>Other gears</td><td rowspan="2">639 tonnes</td></tr><tr><td>88%</td><td>5%</td><td>6%</td><td>1%</td></tr><tr><td colspan="5">539 tonnes</td><td></td></tr></tbody></table>

Bycatch rates are only available for greater North Sea (within the Northeast Atlantic), and only for one metier in latest Working Group on Bycatch of Protected Species (Table 18) (WGBYC; ICES
2022d). Because data on fish species were not consistently submitted to WGBYC in previous years, only 2021 data were used for fish of bycatch relevance (ICES 2022d). That is why days at sea (Das) are so low. Furthermore, rates based on less than 50 days at sea observed should be avoided or at least taken with caution (ICES 2022d).

<table><caption>**Table 18.** Spurdog bycatch rates (no. of animals per day) and 95% confidence intervals around the rates provided by métier level 4 for 2021. Days at Sea (Das) refers to observed effort while coverage (not always available) refers to the % of days observed respect to total effort.</caption><thead><tr><th>Region</th><th>Metier</th><th>Das</th><th>Coverage</th><th>No. of animals</th><th>rate</th><th>CI5-CI95</th></tr></thead><tbody><tr><td>Greater North Sea</td><td>GNS</td><td>29</td><td>--</td><td>3</td><td>0.103</td><td>0.034-0.206</td></tr></tbody></table>

Additional bycatch rates, with a higher number of observed days, can be found in the Working Group on Bycatch of Protected Species of 2020 (ICES 2020a), although these are provided by métier 3 and ICES area (Table 19).

<table><caption>**Table 19.** Spurdog bycatch rates (no. of animals per day) derived from the ICES WGBYC data call for 2018 data. Numbers are provided by métier level 3, region and ICES area. Days at Sea (Das) refers to observed effort while coverage refers to the % of days observed respect to total effort. When rates for more than one métier are given in the same region, mean rate is also provided.</caption><thead><tr><th>Region</th><th>ICES Area</th><th>Metier 3</th><th>Das</th><th>Total effort in days</th><th>Coverage (%)</th><th>No. of animals</th><th>Rate</th><th>Mean rate</th></tr></thead><tbody><tr><td rowspan="2">Bay of Biscay and Iberian Coast</td><td>27.8.a</td><td>Bottom trawls</td><td>581.48</td><td>22051</td><td>2.63</td><td>4</td><td>0.007</td><td>-</td></tr><tr><td>27.8.a</td><td>Nets</td><td>145.86</td><td>10421.11</td><td>1.39</td><td>3</td><td>0.021</td><td></td></tr><tr><td rowspan="2">Celtic Sea</td><td>27.8.b</td><td>Nets</td><td>172.34</td><td>7279.98</td><td>2.36</td><td>1</td><td>0.006</td><td>0.013±0.010</td></tr><tr><td>27.6.a</td><td>Bottom trawls</td><td>259.15</td><td>23117.75</td><td>1.12</td><td>102</td><td>0.212</td><td></td></tr><tr><td></td><td>27.7.a</td><td>Bottom trawls</td><td>339.43</td><td>15029.09</td><td>2.26</td><td>619</td><td>1.824</td><td></td></tr><tr><td></td><td>27.7.f</td><td>Bottom trawls</td><td>120.87</td><td>11138.26</td><td>1.08</td><td>2</td><td>0.017</td><td></td></tr><tr><td></td><td>27.7.h</td><td>Bottom trawls</td><td>860.62</td><td>11591.21</td><td>7.42</td><td>25</td><td>0.029</td><td>0.357±0.722</td></tr><tr><td></td><td>27.7.g</td><td>Bottom trawls</td><td>477.18</td><td>24146.81</td><td>1.98</td><td>84</td><td>0.176</td><td></td></tr><tr><td></td><td>27.7.j</td><td>Bottom trawls</td><td>312.84</td><td>11512.01</td><td>2.72</td><td>14</td><td>0.045</td><td></td></tr></tbody></table>
SEAwise - WP4.2 – Thresholds and bycatch rates for PET species

<table><tbody><tr><td></td><td>27.6.a</td><td>Longlines</td><td>49</td><td>2805.17</td><td>1.75</td><td>2</td><td>0.041</td><td>-</td></tr><tr><td></td><td>27.6.a</td><td>Pelagic trawls</td><td>124</td><td>2300.53</td><td>5.39</td><td>3</td><td>0.024</td><td>-</td></tr><tr><td></td><td>27.7.a</td><td>Nets</td><td>5</td><td>353.19</td><td>1.41</td><td>7</td><td>1.4</td><td></td></tr><tr><td></td><td>27.7.f</td><td>Nets</td><td>66</td><td>2695.08</td><td>2.45</td><td>17</td><td>0.258</td><td></td></tr><tr><td></td><td>27.7.g</td><td>Nets</td><td>63</td><td>2302.47</td><td>2.73</td><td>423</td><td>1.27</td><td>1.802±2.467</td></tr><tr><td></td><td>27.7.h</td><td>Nets</td><td>29.58</td><td>1168.51</td><td>2.53</td><td>180</td><td>6.08</td><td></td></tr><tr><td></td><td>27.7.j</td><td>Nets</td><td>175</td><td>3200.80</td><td>5.47</td><td>1</td><td>0.006</td><td></td></tr><tr><td rowspan="4">Greater North Sea</td><td>27.4.a</td><td>Bottom trawls</td><td>347.95</td><td>41430.55</td><td>0.83</td><td>3</td><td>0.009</td><td></td></tr><tr><td>27.7.d</td><td>Bottom trawls</td><td>217.46</td><td>28150.30</td><td>0.77</td><td>2</td><td>0.009</td><td>0.014±0.009</td></tr><tr><td>27.7.e</td><td>Bottom trawls</td><td>439.13</td><td>31665.05</td><td>1.38</td><td>37</td><td>0.025</td><td></td></tr><tr><td>27.4.a</td><td>Longlines</td><td>58</td><td>4955.80</td><td>1.17</td><td>1</td><td>0.017</td><td>0.285±0.341</td></tr><tr><td></td><td>27.4.c</td><td>Longlines</td><td>2</td><td>259.31</td><td>0.77</td><td>1</td><td>0.50</td><td></td></tr><tr><td></td><td>27.4.a</td><td>Pelagic trawls</td><td>68</td><td>2022.07</td><td>3.36</td><td>13</td><td>0.191</td><td>-</td></tr><tr><td></td><td>27.7.e</td><td>Nets</td><td>164.52</td><td>11442.16</td><td>1.44</td><td>758</td><td>1.629</td><td>-</td></tr></tbody></table>
## Undulate rate in English Channel

The members of the Superorder Batoidea are widely distributed throughout the Northeast Atlantic Ocean and the Mediterranean Sea (Ebert & Dando 2020) and are exploited by commercial fisheries as target and by-catch species. Generally recognized as K-selected species, they are characterized by slow growth, late sexual maturity, low fecundity and long life, limiting their population's capacity to recover from overfishing (Villagra et al. 2022).

Among the rays fished in European waters, the undulate ray *Raja undulata* is of major concern given its current high discard rate in most northeast Atlantic commercial coastal fisheries. In fact, it is listed as “Endangered” according to the Red List criteria of the International Union for Conservation of Nature (IUCN). Fishing of this species was first prohibited in December 2009 (EC 43/2009) before being assigned a zero total allowable catch (TAC) in December 2013. A small TAC (25 t) for undulate ray was introduced in ICES Division 8 in 2015 and increased to 30 t in 2018 (Morfin et al. 2019).

In 2022, the stock was benchmarked for English Channel (divisions 7d-e) (ICES 2022a). Whereas total biomass was considered during the benchmark, ICES assessment and advice is based only on exploitable biomass (individuals ≥ 50 cm total length)(ICES 2022c).

For this stock, ICES advises that when the MSY approach is applied, landings in 2023 and 2024 should be no more than 4836 and 4675 tonnes respectively (Table 20).

<table><caption>**Table 20** Maximum catches of undulate ray that should not be exceeded for 2023 and 2024 for undulate ray when the MSY approach is applied, as well as the organization/studies that apply or recommend this approach.</caption><thead><tr><th>SPECIES</th><th>METHOD</th><th>YEAR</th><th>THRESHOLD</th><th>ORGANIZATION</th><th>REFERENCE</th></tr></thead><tbody><tr><td rowspan="2">UNDULATE RAY</td><td>MSY</td><td>2023</td><td>4836</td><td rowspan="2">ICES</td><td rowspan="2">ICES (2022c)</td></tr><tr><td>MSY</td><td>2024</td><td>4675</td></tr></tbody></table>

In 2021, 2959 tonnes of undulate ray were caught (Table 21); a small part, 205 tonnes, were landings that come from bottom trawls and nets mainly, while the biggest part, 2754 tonnes, were discards (ICES 2022c). In this species, acoustic tracking revealed that at least the 49% of the rays survived discarding (Morfin et al. 2019). Currently, fishing pressure on the stock is below HR<sub>MSY</sub>, and spawning-stock size is above MSY B<sub>trigger</sub>, B<sub>pa</sub>, and B<sub>lim</sub> (ICES 2022c).

<table><caption>**Table 21.** Undulate ray catch distribution by fleet in 2021 as estimated by ICES for English Channel</caption><thead><tr><th rowspan="2">Total catch</th><th colspan="5">Landings</th><th rowspan="2">Discards</th></tr><tr><th>Beam trawl</th><th>Bottom trawl</th><th>Nets 28%</th><th>Lines</th><th>Other gears</th></tr></thead><tbody><tr><td>2959 tonnes</td><td>6%</td><td>56%</td><td>205 tonnes</td><td>1%</td><td>1%</td><td>2754 tonnes</td></tr></tbody></table>
Bycatch rates are only available for greater North Sea in latest Working Group on Bycatch of Protected Species (Table 22) (WGBYC; ICES 2022d). Because data on fish species were not consistently submitted to WGBYC in previous years, only 2021 data were used for fish of bycatch relevance (ICES 2022d). That is why days at sea (Das) are so low. Furthermore, rates based on less than 50 days at sea observed should be avoid or at least taken with caution (ICES 2022d).

<table><caption>**Table 22.** Undulate ray bycatch rates (no. of animals per day) and 95% confidence intervals around the rates provided for the Mediterranean basin by métier level 4 for 2021. Days at Sea (Das) refers to observed effort while coverage (not always available) refers to the % of days observed respect to total effort.</caption><thead><tr><th>Region</th><th>Metier</th><th>Das</th><th>Coverage</th><th>No. of animals</th><th>rate</th><th>CI5-CI95</th></tr></thead><tbody><tr><td rowspan="3">Greater North Sea</td><td>GTR</td><td>13</td><td>--</td><td>55</td><td>4.230</td><td>3.307-5.153</td></tr><tr><td>TBB</td><td>95</td><td>--</td><td>48</td><td>0.506</td><td>0.390-0.633</td></tr><tr><td>GNS</td><td>27</td><td>--</td><td>11</td><td>0.407</td><td>0.222-0.629</td></tr></tbody></table>

Additional bycatch rates, with a higher number of observed days, can be found in the Working Group on Bycatch of Protected Species of 2020 (ICES 2020a), although these are provided by métier 3 and ICES area (Table 23).

<table><caption>**Table 23.** Undulate ray bycatch rates (no. of animals per day) derived from the ICES WGBYC data call for 2018 data. Numbers are provided by métier level 3, region and ICES area. Days at Sea (Das) refers to observed effort while coverage refers to the % of days observed respect to total effort. When rates for more than one métier are given in the same region, mean rate is also provided.</caption><thead><tr><th>Region</th><th>ICES Area</th><th>Metier 3</th><th>Das</th><th>Total effort in days</th><th>Coverage (%)</th><th>No. of animals</th><th>Rate</th><th>Mean rate</th></tr></thead><tbody><tr><td rowspan="6">Bay of Biscay and Iberian Coast</td><td>27.8.a</td><td>Bottom trawls</td><td>581.48</td><td>22051</td><td>2.63</td><td>37</td><td>0.064</td><td rowspan="6">0.125±0.092</td></tr><tr><td>27.8.b</td><td>Bottom trawls</td><td>41.88</td><td>10759.01</td><td>0.39</td><td>11</td><td>0.263</td></tr><tr><td>27.8.c</td><td>Bottom trawls</td><td>94</td><td>11049.86</td><td>0.85</td><td>7</td><td>0.074</td></tr><tr><td>27.9.a</td><td>Bottom trawls</td><td>149</td><td>50861.49</td><td>0.29</td><td>15</td><td>0.101</td></tr><tr><td>27.8.a</td><td>Nets</td><td>145.86</td><td>10421.11</td><td>1.39</td><td>64</td><td>0.439</td><td rowspan="2">0.916±0.674</td></tr><tr><td>27.8.b</td><td>Nets</td><td>172.34</td><td>7279.98</td><td>2.36</td><td>240</td><td>1.393</td></tr><tr><td rowspan="2">Celtic Sea</td><td>27.8.b</td><td>Longlines</td><td>11.63</td><td>2813.75</td><td>0.41</td><td>3</td><td>0.258</td><td rowspan="2">-</td></tr><tr><td>27.7.f</td><td>Nets</td><td>66</td><td>2695.08</td><td>2.45</td><td>1</td><td>0.015</td><td>0.126±0.156</td></tr></tbody></table>
SEAwise - WP4.2 – Thresholds and bycatch rates for PET species

<table><tbody><tr><td></td><td>27.7.h</td><td>Nets</td><td>29.58</td><td>1168.51</td><td>2.53</td><td>7</td><td>0.237</td><td></td></tr><tr><td></td><td>27.7.h</td><td>Bottom trawls</td><td>860.62</td><td>11591.21</td><td>7.42</td><td>2</td><td>0.002</td><td>-</td></tr><tr><td rowspan="2">Greater North Sea</td><td>27.7.d</td><td>Bottom trawls</td><td>217.46</td><td>28150.30</td><td>0.77</td><td>69</td><td>0.317</td><td></td></tr><tr><td>27.7.e</td><td>Bottom trawls</td><td>439.13</td><td>31665.05</td><td>1.38</td><td>67</td><td>0.153</td><td>0.235±0.115</td></tr><tr><td></td><td>27.7.d</td><td>Nets</td><td>131</td><td>11816.96</td><td>1.11</td><td>129</td><td>0.985</td><td></td></tr><tr><td></td><td>27.7.e</td><td>Nets</td><td>164.52</td><td>11442.16</td><td>1.44</td><td>6</td><td>0.036</td><td>0.510±0.671</td></tr><tr><td></td><td>27.7.d</td><td>Pelagic trawls</td><td>55.81</td><td>1006.72</td><td>5.54</td><td>24</td><td>0.430</td><td></td></tr><tr><td></td><td>27.7.d</td><td>Seines</td><td>9.78</td><td>3365.50</td><td>0.29</td><td>2</td><td>0.205</td><td>0.232±0.185</td></tr><tr><td></td><td>27.7.e</td><td>Dredges</td><td>16</td><td>10038.48</td><td>0.16</td><td>1</td><td>0.063</td><td></td></tr></tbody></table>
## Longnose spurdog in the Mediterranean

The longnose spurdog, *Squalus blainville* is a demersal shark inhabiting depths to about 700 m, extending from tropical to temperate waters of the Atlantic, Pacific, and Indian Oceans, including the Mediterranean and the Black Sea (Compagno et al. 2005). In the Mediterranean Sea, *S. blainville* is a usually taken as bycatch in bottom trawling and long line vessels, and then marketed for human consumption; however official records of its landings are not available. Indeed, the IUCN categorizes it as Data Deficient (DD) (Dulvy et al. 2016), because of the paucity of information regarding the abundance, distribution and biological traits of the species. However, there is growing concern over the extent of shark catches in the Mediterranean, as their K-selected life-history characteristics make them intrinsically vulnerable to fishing pressure (Dulvy et al. 2016). The longnose spurdog presents a low growth rate and a long life span (> 10 years) (Marouani et al. 2012, Kousteni & Megalofonou 2015), low fecundity and great length at first maturity (Kousteni & Megalofonou 2011, Marouani et al. 2012, Anastasopoulou et al. 2017, Donnaloia et al. 2022).

The size and demographic structure of longnose spurdog populations are poorly known. Thus, to estimate the population size we used the MEDITS survey density index (Spedicato et al. 2019) from data collected within 11 years (2009-2019) in South Adriatic Sea (GSA18, Fig. 5), and between 2014 and 2021 in the eastern Ionian Sea (GSA20, Fig. 6). In GSA 18 the last two years were excluded because in those surveys the areas (east part of South Adriatic) where this species is more present were not sampled. In order to obtain the number of longnose spurdog population in each area, the average density index was estimated. In GSA18, the average density index was 5.38 ind/km² and the average population size 156,075 shark specimens. In GSA20, the average index was calculated based on the hauls (presence and absence in the area) for a total of 6 years of surveys. The estimation was 38.04 ind/km² and the population size 639,948 individuals (Table 24).
<figure><img src="image_188.png" /><figcaption>Figure 5 – Medits survey density index for S. blainville in south Adriatic Sea (GSA 18)</figcaption></figure>

<figure><img src="image_189.png" /><figcaption>Figure 6 – Medits survey density index for S. blainville in the eastern Ionian Sea (GSA 20)</figcaption></figure>

For the PBR calculation, we applied the mean abundance estimation per year considering the 20th percentile of the 11 years in GSA18 (Nmin= 33,564), whereas the hauls were taken into account for 6 years in GSA20 (Nmin= 525,275). As a recovery factor, Fr was set at 0.5 as default, which is used for threatened species or with unknown status. For the productivity rate (Rmax) we used the average value calculated for another species of the same genus (Squalus acanthias), from two areas of the Atlantic Ocean (Cortés 2016) (Table 24).
<table><caption>**Table 24.** Bycatch thresholds estimated through PBR approach. Parameters needed to estimate the thresholds are also included as well as the organisms and/or studies that apply them.</caption><thead><tr><th>Species/Population</th><th>Method</th><th>N</th><th>Nmin</th><th>Rmax</th><th>Fr</th><th>Threshold</th><th>Organization</th></tr></thead><tbody><tr><td>Longnose spurdog<br>GSA 18</td><td>PBR</td><td>156,075</td><td>33,564</td><td>0.057</td><td>0.5</td><td>478</td><td>--</td></tr><tr><td>Longnose spurdog<br>GSA 20</td><td>PBR</td><td>639,948</td><td>525,275</td><td>0.057</td><td>0.5</td><td>7,485</td><td>--</td></tr></tbody></table>
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## 9. Document Information

<table><tr><td>EU Project</td><td>No 862428</td><td>Acronym</td><td>SEAwise</td></tr><tr><td>Full Title</td><td colspan="3">Shaping ecosystem based fisheries management</td></tr><tr><td>Project website</td><td colspan="3">https://www.seawiseproject.org/</td></tr></table>

<table><tr><td>Deliverable</td><td>N°</td><td>D6.7</td><td>Title</td><td>Consistency of existing targets and limits for indicators in an ecosystem context</td></tr><tr><td>Work Package</td><td>N°</td><td>6</td><td>Title</td><td>Evaluation of fisheries management strategies in an ecosystem context</td></tr><tr><td>Work Package Leader</td><td colspan="4">Dorleta García</td></tr><tr><td>Work Participants</td><td colspan="4">Kempf, A., Taylor, M., Kühn, B., Brown, E., Trijoulet, V., Vinther, M., Girardin, R., Savina-Rolland, M., Lehuta, S., Halouani, G., Robert, M., Woillez, M., Mahevas, S., Travers, M., Andres, M., Garcia, D., Ibaibarriaga, L., Sánchez-Maroño, S., Astarloa Diaz, A., Batts, L., Reid, D., Bitetto, I., Spedicato, M.-T., Romagnoni, G., Giannoulaki, M., Sgardeli, V., Tsoukali, S., Liontakis, A., Vassilopoulou, C., Millar, S., Depestele, J., van Hoey, G., Piet, G., Hamon, K., Kraan, M., Smout. S., Ransijn, J., Thorpe, R., Lynam, C., Bluemel, J., Voss, R., Ojaveer, H., Hommik, K., Melia, P., Gascuel, D., Potier, M., Ustups, D., Plikss, M., Heath, M., Poos, J.-J., Binch, L., and Rindorf, A.</td></tr></table>

<table><tr><td>Lead Beneficiary</td><td>Thuenen Institute of Sea Fisheries (TI-SF), P9</td></tr><tr><td>Authors</td><td>Kempf, A., Taylor, M., Kühn, B., Brown, E., Trijoulet, V., Vinther, M., Girardin, R., Savina-Rolland, M., Lehuta, S., Halouani, G., Robert, M., Woillez, M., Mahevas, S., Travers, M., Andres, M., Garcia, D., Ibaibarriaga, L., Sánchez-Maroño, S., Astarloa Diaz, A., Batts, L., Reid, D., Bitetto, I., Spedicato, M.-T., Romagnoni, G., Giannoulaki, M., Sgardeli, V., Tsoukali, S., Liontakis, A., Vassilopoulou, C., Millar, S., Depestele, J., van Hoey, G., Piet, G., Hamon, K., Kraan, M., Smout. S., Ransijn, J., Thorpe, R., Lynam, C., Bluemel, J., Voss, R., Ojaveer, H., Hommik, K., Melia, P., Gascuel, D., Potier, M., Ustups, D., Plikss, M., Heath, M., Poos, J.-J., Binch, L.,</td></tr><tr><td>Reviewers</td><td>Anna Rindorf</td></tr></table>

<table><tr><td>Due date of deliverable</td><td>31.03.2023</td></tr><tr><td>Submission date</td><td>28.03.2023</td></tr><tr><td>Dissemination level</td><td>PU<fnref n="1" /></td></tr><tr><td>Type of deliverable</td><td>R<fnref n="2" /></td></tr></table>

<table><thead><tr><th colspan="4">Version log</th></tr><tr><th>Issue Date</th><th>Revision N°</th><th>Author</th><th>Change</th></tr></thead><tbody><tr><td>20.03.2023</td><td></td><td>Alexander Kempf and Marc Taylor</td><td>First version</td></tr><tr><td>27.03.2023</td><td>0.1</td><td>Anna Rindorf</td><td>First QA</td></tr><tr><td>28.03.2023</td><td>1.0</td><td>Alexander Kempf and Marc Taylor</td><td>QA edits incorporated</td></tr><tr><td>31.12.2023</td><td>1.1</td><td>Anna Rindorf</td><td>Added doi</td></tr></tbody></table>

<footnote n="1">¹Dissemination level: PU: Public</footnote>

<footnote n="2">² Nature of deliverable: R: Report</footnote>
<figure><img src="image_190.png" /></figure>