Trawler Engine Size Had No Effect on Baltic Herring Size/Age Structure: An Experimental Study in the Gulf of Riga, Baltic Sea

Elor Sepp,Tiit Raid,Timo Arula,Markus Vetemaa

doi:10.3390/fishes7010046

Abstract

The Gulf of Riga stock of Baltic herring (Clupea harengus membras L.) has been maintained through several management tools. One such tool is the restriction of vessels’ main engine power (<221 kW). This restriction was implemented in the early 1990s and is based on the vessel types available in the area and on the assumption that the gear size used in trawl fishery depends on the vessel size (power). In the current study, we compared vessels with different engine powers using the same gears currently allowed in the gulf, to identify whether vessel power had any relation to catch structure. The results showed that engine power did not explain the differences in catch structure, which were more dependent on season and depth of water. Easing the power restriction of the trawl vessels in the Gulf of Riga will most likely not have a major negative impact on the sustainable management of the herring population. However, vessels with higher engine power should not use larger trawl gear than is currently used in the gulf.

Highlights

The management success of fish stocks depends on the availability and reliability of knowledge surrounding the biological specifics of the stock, as well as on fishery-dependent information
The results showed that engine power did not explain the differences in catch structure, which were more dependent on season and depth of water
A 30-day ban of trawl fishery during the main spawning migration in spring has been imposed in both Latvia and Estonia, a summer ban of trawl fishery in the Estonian part of the Gulf [15], the prohibition of fishing with trawls in waters of less than 20 m in depth, a maximum trawl height of 12 m, and a minimum cod-end mesh size of at least 16 mm [20,21] serve as examples of such measures. These restrictions include a maximum engine power limit of 300 HP (221 kW) for trawl vessels operating in the Gulf of Riga (GoR), in order to avoid the deployment of large high-seas trawl vessels which might seriously affect the fragile ecosystem of the shallow and spatially restricted GoR [21]

Summary

Introduction

The management success of fish stocks depends on the availability and reliability of knowledge surrounding the biological specifics of the stock, as well as on fishery-dependent information. A 30-day ban of trawl fishery during the main spawning migration in spring has been imposed in both Latvia and Estonia, a summer ban of trawl fishery (from mid-June to September) in the Estonian part of the Gulf [15], the prohibition of fishing with trawls in waters of less than 20 m in depth, a maximum trawl height of 12 m, and a minimum cod-end mesh size of at least 16 mm [20,21] serve as examples of such measures These restrictions include a maximum engine power limit of 300 HP (221 kW) for trawl vessels operating in the GoR, in order to avoid the deployment of large high-seas trawl vessels which might seriously affect the fragile ecosystem of the shallow and spatially restricted GoR [21]. We hypothesized that more powerful vessels do not cause harm to the stock when using the same gear as less powerful vessels

Materials and Methods

Discussion

Findings

Conclusions