What is the release mortality rate for European sea bass caught by anglers?

(Latest update: 13 December 2015, 14:30)

Nobody knows for sure, as nobody has studied this issue. Nevertheless, ICES makes use of an assumed release mortality of 20%. The EAA strongly disagrees with that percentage based on evidence shown further below that the release rate on average cannot be more than max. 9%, most likely less.

This is not a trivial issue as the European sea bass is in trouble and fishing mortality has to be reduced within both commercial and recreational fisheries. Anglers release many of the bass they catch, 20-64% (see page 6; ICES, June 2015), which is a good thing as this brings down the mortality rate substantially. How much depends on the survival rate of the released fish of course. The release mortality rate is part of the legislators knowledge base when they shall decide about next year's bag limit, if it shall remain 3 bass as today or be reduced to two, one or zero. (The Commission has suggested (Nov 2015) zero recreational fishing for bass first half of 2016, and a one bass only bag limit during second half of 2016. The ministers shall decide 14-15 December).

Bass angling has suffered for years the depletion of the bass stock since commercial fisheries took off in the 1970s and 80s. Irish waters were the first to be overfished to the extent that a ban on commercial fishing for bass was introduced in 1990, which is still in force today.

We cannot accept that the anglers now have to pay disproportionally for a problem not caused by them in the first place. It is important that the catch, landings, discards and release mortality figures are fairly accurate, which is not the case today. Here we only look at the release mortality for angling to try to get closer to the "real" percentage (which is lower than 20%) - but the other issues mentioned are as, or more, important to investigate.

We fully agree with scientists, that (see here, page 1): “..as the survival rates of European marine species are mostly unknown, there is a need to conduct post-release survival studies and to identify factors affecting post-release survival.”

Case 1:

ICES (2012; page 133): "Implications of missing recreational catches in assessment model"

- Recreational catch estimates for sea bass are currently available for only 2010, and only for France and the Netherlands. Data for surveys in the UK in 2012 are not yet available. For France and Netherlands, the combined estimates of recreational fishery removals for 2010, including an assumed hooking mortality of 20% for released fish, is 1115 t.

EAA comment:
If the release mortality was set to 10% the total removals would be:

France: 973 tonnes
Netherlands:102 tonnes
Total removed: 1075 tonnes

If the release mortality was set to 5% the total removals would be:

France: 956 tonnes
Netherlands: 99 tonnes
Total removed: 1055 tonnes

NB! These figures are just meant to illustrate the impact of various release mortality rates. These are outdated 2010 figures. ICES has estimated recreational fisheries landings in 2014 to 908 tonnes (FR, UK, BE, NL). The minimum landing size was increased from 36cm to 42 cm in France three years ago, and in September this year for the rest of the Northern Atlantic are. A bag limit, three bass per recreational fisher per day, was introduced 29 March this year. Thus - everything else equal - the recreational landings will be less than 908 tonnes this year and decline further next year (with or without additional management measures).
Release rates in the past have varied between countries and from one year to another according to ICES. France has had the lowest release rate, 20% and Netherlands the highest, 64%. The increase of the minimum landing size this year should, logically, increase the portion of bass released (increase the release rates).

Case 2:

ICES Journal of Marine Science Advance Access published July 21, 2013

"Unexpectedly high catch-and-release rates in European marine recreational fisheries: implications for science and management"

- "Since 2009, all EU member states are obligated to evaluate recreational catches of Atlantic cod, European eel (Anguilla anguilla), Atlantic salmon (Salmo salar), European sea bass, and Atlantic bluefin tuna (Thunnus thynnus) in relevant regions."

- "Although not further specified, the Commission regulation instructs member states to collect data to estimate marine recreational catches... commonly defined as harvested and released fish... However, while catch-and-release (C&R) practices have been thoroughly studied in marine and freshwater recreational fisheries in the USA, Canada and Australia, and for a few freshwater fisheries in Europe..., only very few peer-reviewed publications exist on C&R practices in European marine recreational fisheries (e.g. Alo´s, 2008; Alo´s et al., 2009a, 2009b; Veiga et al., 2011; Ferteret al., 2013; Weltersbach and Strehlow, 2013)."

EAA comment: We have taken a closer look at four of the six papers mentioned above:

1) - Alo´s et al., 2009a: “Influence of anatomical hooking depth, capture depth, and venting on mortality of painted comber (Serranus scriba) released by recreational anglers".
ICES Journal of Marine Science, 65: 1620–1625.

Page 1: “Immediate (4–5 h) and delayed (10 d) hooking mortality for released fish kept in tanks was evaluated for painted comber (Serranus scriba) taken by the recreational fishery of the Balearic Islands (western Mediterranean). Results showed low rates of immediate (10.8%) and delayed (3.3%) hooking mortality, a total mortality of 14.1%. (..) Therefore, the results confirm that a practice of catch-and-release (voluntary or mandatory) for S. scriba needs to be promoted among recreational anglers.”

2) - Alo´s, J., Palmer, M., and Grau, A. M. 2009b: “Mortality of Diplodus annularis and Lithognathus mormyrus released by recreational anglers: implications for recreational fisheries management.
Fisheries Management and Ecology, 16: 298 –305

Cutting from the abstract:
“The circumstances of the catch, such as capture depth, water temperature, fish size, hook type, hook location, bleeding, unhooking time and cutting the hook line were tested with a logistic regression model. Diplodus annularis experienced moderate rates of mortality (15%), (..) By contrast, L. mormyrus exhibited higher mortality rates (33%) with over 90% of the catch under the minimum legal size. Deep-hooking was the strongest predictor of mortality. When circle hooks were used, or if the line was cut when the fish were deep-hooked, mortality was considerably reduced. Strategies, such as promoting the use of more selective gears that reduce the capture of undersized fish and implementing gentler release techniques, should be considered in managing these species.”

3) - Veiga, P., Goncalves, J. and Erzini, K. 2011: “Short-term hooking mortality of three marine fish species (Sparidae) caught by recreational angling in the south Portugal.
Fisheries Research, 108: 58 –64

Cutting from the abstract:
“Short-term hooking mortality was evaluated for three sparid species [Diplodus vulgaris(Geoffroy Saint-Hilaire), Sparus aurata L. and Spondyliosoma cantharus (L.)] in the Algarve, south Portugal. Fishes were caught from the shore during October 2009 at a fish farm reservoir (Ria Formosa), using three different hook sizes. The relationships between hooking mortality and seven independent variables were analyzed using logistic regression models. In all, 384 fishes representing the three target species were caught during the angling sessions. (..) Mortalities ranged between 0% for D. vulgaris and 12% for S. aurata (S. cantharus, 3%). Our results support the current mandatory practices of releasing undersized fish for the studied species, given the low post-release mortality rates observed.”

4) - Weltersbach and Strehlow, 2013; Weltersbach, M. S., and Strehlow, H. V. 2013. “Dead or alive – estimating post-release mortality of Atlantic cod in the recreational fishery." ICES Journal of Marine Science.

Cutting from the abstract:
“This study investigates (i) the post-release mortality of undersized cod, (ii) potential factors affecting mortality, and (iii) consequences of the catch-and-release process on cod. During four experimental trials, western Baltic Sea cod were angled from a charter vessel and thereafter observed together with control fish in netpens for 10 d at holding temperatures between 6.2 and 19.88C. Adjusted mortality rates for angled cod ranged from 0.0–27.3% (overall mean 11.2%).”
Cuttings from the text: “Discussion – Mortality: The post-release mortality rate (adjusted for handling and caging effects) for angled cod ranged from 0.0 –27.3% (overall mean 11.2%). This overall mean mortality rate was close to the average release mortality rate of 18% calculated by Bartholomew and Bohnsack (2005), who carried out a meta-analysis of 274 catch-and-release mortality studies.”… Conclusions and implications: This study can be considered a first step in closing the existing scientific gap in investigating possible post-release mortalities and the consequences of catch-and-release on cod in the recreational fishery. Our findings suggest that a substantial amount of recreationally released cod survive and thus cannot be classified as removals from the western Baltic cod stock. However, the present post-release mortality rates should only serve as first estimations. The results have to be viewed with great caution on a population/stock level, as post-release mortality estimates derived from containment experiments cannot accurately predict recreational fishing mortality of a population in its natural environment.”

Case 3:

Report of the Inter-Benchmark Protocol on New Species (Turbot and Sea bass; IBPNew 2012)

It is said on page 97:
1) - “Striped bass are very similar to European sea bass in terms of morphology, habitats and angling methods.”

EAA comment: That is not entirely accurate. Striped bass is an anadromous fish - migrates between sea- and freshwaters. Spawning takes place in freshwater. European sea bass is a marine fish, which spawns at sea.

2) - “The US National Marine Fisheries Service has in the past used an average hooking mortality of 9% for striped bass, estimated by Diodati and Richards (1996).”

EAA comment: The 9% mortality is the result from an experiment carried out in a saltwater pond with an average depth of approximately 3 m and surface water temperature ranging from 15 to 28°C. The paper is here. It is important to make the distinction between saltwater and freshwater conditions, when doing experiments with striped bass, as: "Predicted as well as observed mortality for the entire experimental group was 9% which is generally much lower than reported in striped bass hooking mortality studies conducted in freshwater". The experiment mimic bass angling under sea water conditions. It was concluded, that: “Mean predicted mortality was 26% for the worst set of conditions, 9% for the intermediate set, and 3% for the best set (Table 4).”)

We find it fair to say that - everything considered - the experimental setup doesn't mimic exactly European sea angling under natural conditions e.g. the water temperatures seem above what would be normal for Northern European sea bass. So, even 9% is a fairly low mortality rate we would expect a release mortality rate for Northern sea bass to be below 9%.

3) – “A literature review of hooking mortality for a range of species compiled by the Massachusetts Division of Marine Fisheries included a total of 40 different experiments by 16 different authors where striped bass hooking mortality was estimated over two or more days (Gary A. Nelson, Massachusetts Division of Marine Fisheries, pers. comm.) The mean hooking mortality rate was 0.19 (standard deviation 0.19)”

EAA comment: We haven't looked into this as yet but we find it hard to believe that 40 different striped bass experiments would show a mean hooking mortality rate of 0.19. We would like to know more about these experiments and papers before we say more about that. We also find it confusing that everything said above is from a chapter (page 97) titled "Hooking mortality, and mortality of discarded bass from commercial vessels". We wonder if the 40 experiments are all genuine recreational angling experiements or include commercial line fishing as well? In any case, conclusions from experiments with striped bass angling in freshwaters, or fresh- and seawaters, should be moderated to show only results for seawater angling before making any comparison with European sea bass angling.
In the USA, the Atlantic States Marine Fisheries Commission currently applies an 8% mortality rate for striped bass caught and released by recreational anglers in saltwater ecosystems.

Case 4:

Catch and Release Fishing Effectiveness and Mortality; by P. Reiss et al. (2003)

This is a review paper written in response to a request by a Brazilian government agency for an analysis of catch and release mortality data in the current scientific literature and ways to minimize mortality in real-world field applications. The paper gives an overview of survival rates from a wide variety of species:
Table 1
Summary of Results of Catch and Release Mortality Studies
(Without Consideration of Optimized Techniques)

EAA comment: It is worth noticing that the highest mortality rate is 5.8%, and 4.3% for striped bass, inshore.

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