Bait Digging Research Articles

Estimated footprint of shellfishing activities in Zostera noltei meadows in a northern Spain estuary: Lessons for management

Intertidal seagrasses often occupy areas of high ecological importance that are also targeted for human activities, such as shellfishing and leisure walking. These activities could affect the growth or survival of seagrass. The society at large lacks knowledge of the ecological relevance of seagrasses and their vulnerability, presenting an obstacle for their conservation. Here, the Oka estuary (Basque Country, N. Spain) is used as a case study to analyse the spatial extent of shellfishing activities in seagrass (Zostera noltei). This estuary holds 84% of the intertidal seagrass meadows present in the Basque Country and is visited during the year by professional and recreational shellfishers. Bait digging is legal year-round, and clam digging (by professionals only) from October to February. Human presence over 11 years averaged 17 people on the tidal flat in each daylight hours from August to October. Each professional shellfishing daily trip affected 7.4–21.6 m2 by fishing and 110–188 m2 by trampling in seagrass, but was substantially different between clam and bait (crustacean, worm) fishing. Scaling up this area to estimated annual number of shellfishers, 8–69% of the total seagrass area is trampled and 1–9% is dug per year. In comparison to a habitat suitability map for seagrass, 98% of trampling occurred within a very highly suitable area for seagrass presence (i.e., >90%). This pressure could adversely affect seagrass density and prevent the expansion of meadows into areas suitable for seagrass. Management of public impacts to seagrass in this estuary could occur through prohibition of some activities in seagrass and awareness campaigns among shellfishers and walkers.

Spatially modelling the suitability, sensitivity, and vulnerability of data poor fisheries with GIS: A case study of the Northumberland lugworm fishery

Data on fishers' spatial distribution are vital, driven by a requirement for evidence-based management, and the trend towards Marine Spatial Planning. Intertidal fisheries have received considerably less attention from managers and scientists, compared to inshore and offshore counterparts to date. The need for additional intertidal fisheries data to inform management, specifically within European Marine Sites, has been identified. The purpose of this study is to map the spatial distribution of the data-poor Northumberland lugworm fishery, relating this to the sensitive features, habitats, and species present within the Berwickshire and North Northumberland Coast European Marine Site (BNNC EMS), ultimately mapping the vulnerability of areas to lugworm bait digging. Suitability, sensitivity, and vulnerability to the lugworm fishery were spatially modelled using cost-effective methodologies. Weighted Linear Combination models were created using both collated (e.g. sediment type, conservation designations) and collected data (e.g. lugworm density and size). Data processing was undertaken in GIS, and criteria weightings were assigned from expert interviews. Model outputs revealed the most intensely harvested sites (most suitable), the areas which contained the most sensitive habitats or species (most sensitive), and the sites which were most likely to be impacted by the lugworm fishery (most vulnerable). Extant spatial management measures within the BNNC EMS (e.g. byelaws) were found to encompass the majority of the most vulnerable areas identified, with exceptions highlighted for marine managers. There is scope for methods to be developed further, for additional intertidal fisheries and localities, as a useful management tool where spatial data are lacking.

Polychaete annelids as live bait in Portugal: Harvesting activity in brackish water systems

Polychaete annelids are some of the most heavily harvested invertebrates collected in coastal areas and estuaries for their economic value as live fishing bait or as food supplement in aquaculture activities. However, information on bait digging in Portugal is scarce or incomplete. Thus, the present study aimed at investigating the bait digging activity in the four most relevant brackish water systems in Portugal: Ria de Aveiro and Ria Formosa coastal lagoons and Tagus and Sado estuaries. Direct observations were performed in each brackish water system 1 h and a half before and after the diurnal low spring tide (<0.8 m height), on working days. Additionally, logbooks were delivered to bait diggers and two types of surveys were conducted in every system: one to all the intertidal users and the other only to bait diggers.The estimated daily weighted number of bait diggers varied between 31 in the Tagus estuary and 69 in the Ria Formosa coastal lagoon. Diopatra neapolitana (Delle Chiaje, 1841) was the main target species in Ria de Aveiro (more than 83%), Tagus estuary (more than 60%) and Ria Formosa (more than 90%), while in Sado estuary most of the bait diggers targeted Marphysa sp. (92.6%). The highest and lowest amount of polychaete annelid catches were estimated for Ria de Aveiro coastal lagoon (almost 50 tons per year) and Tagus estuary (11 tons per year), respectively. A total annual bait catch value in these four systems was estimated as €3.84 millions. The most important brackish water systems concerning bait diggers’ number and bait captures were Sado estuary and Ria de Aveiro coastal lagoon where management measures should be considered, although managing polychaete harvesting activity is still difficult due to limited information on harvesting and on direct and indirect impacts on population dynamics.

Introducing a Regulatory Policy Framework of Bait Fishing in European Coastal Lagoons: The Case of Ria de Aveiro in Portugal

The harvesting of bait through digging in coastal mudflats is practiced for recreational and commercial purposes in European coastal systems including the Ria de Aveiro coastal lagoon on the northwest Atlantic coast of Portugal. The scale of harvesting in the Ria de Aveiro has recently increased due to the current economic climate in Portugal, with targeting of the polychaete, Diopatra neapolitana species or “casulo” as it is widely known in the Aveiro region. The national authorities have attempted to control casulo digging by issuing a regulation (Ordinance) in 2014 on the maximum daily catch limit to be caught by each individual. The daily catch limit is intended to represent the Maximum Sustainable Yield (MSY) for casulo beyond which overfishing will occur. The monitoring of the regulatory measures is expected to be conducted through on-site inspections in the digging areas. However, weak law enforcement was noticed, while there is also controversy over the daily catch limit (quota) stipulated by the Ordinance. To this end, the current study attempted to assess digging activities through remote monitoring and random inspections for a better policy enforcement of the national regulation. In addition, different harvesting scenarios were employed through a simplified bioeconomic model to attribute the current and future harvesting trends of bait digging in Aveiro coastal lagoon. The study findings indicate that remote monitoring coupled with some onsite interviews could be a more effective approach for the implementation of the current bait digging policy. Further, the results point to a distinctive discrepancy between the daily catch amount (MSY) introduced by the national legislation and the study findings which should be further scrutinized. The diggers seem to have reached the sustainable harvest identified by the present research. The current economic hardship in Portugal and the low profitability in similar employment sectors will possibly attract more diggers and increase harvesting in the near future. An increased harvest would likely trigger overfishing of D. neapolitana with unknown consequences for the population of the species as well as the aquatic ecosystem. The socio-economic and environmental effects are yet to be further clarified with more detailed data and advanced modeling techniques to ensure the sustainability of the activity.

Distribution and status of Zostera capensis in South African estuaries — A review

This review collates the available knowledge on the distribution and area covered by eelgrass Zostera capensis and shows that it has a wide distribution occurring in 62 estuaries from the Olifants Estuary on the west coast to Kosi Bay on the east coast. It has protected meristems, a strong root system and flexible leaves which enable it to grow under strong tidal conditions as well as tolerate periods of exposure and desiccation characteristic of the intertidal zone. Estuaries with the largest areas of Z. capensis are Olifants, Langebaan, Berg, Knysna, Keurbooms, Swartkops and Bushmans. Only Langebaan and Knysna have some formal protection status. Large populations were lost from KwaZulu-Natal estuaries at the time of Durban Bay harbour development in the 1950s and more recently from St Lucia. There have been a number of studies in South Africa showing the utilisation of eelgrass beds by a variety of invertebrate and fish species for habitat, shelter, foraging sites and nurseries. Fewer studies have addressed nutrient recycling and other ecosystem services such as carbon sequestration. In all estuaries the distribution of Z. capensis is highly dynamic and therefore difficult to map, assess changes over time and use as an indicator of estuary health. Cover and biomass are removed after large floods and have been shown to fluctuate in response to bait digging and disturbance by boats. This review identifies eutrophication as an emerging threat that encourages macroalgal growth, which smothers Z. capensis. Despite its wide distribution range, Z. capensis is sensitive to human impacts which have led to the species being listed as vulnerable in the Red Data List. It is encouraging that approximately 46% of all estuaries with Z. capensis have estuary management plans as these strive to protect sensitive habitats using activity zoning. Studies tracking the changes over time of the Z. capensis beds in specific estuaries are needed to understand dynamic responses. In addition there is urgency for a national assessment of the distribution and health of this keystone species in South Africa.

Short-term impact of bait digging on intertidal macrofauna of tidal mudflats around the Kneiss Islands (Gulf of Gabès, Tunisia)

In the Gulf of Gabes (South-eastern Tunisia), polychaete bait digging is widely practiced for recreational and commercial fishing and is an economically significant activity. The present study aims to assess the short-term effects of intertidal bait digging on macrobenthic communities from the Kneiss Islands. Following a protocol with a control station (not impacted) and three impacted stations for polychaete collection, the study was conducted during March and April 2015 at spring tides. After digging, immediate significant decreases were observed in the abundance of total macrofauna as well in numerous families of polychaetes. Control of this activity should be proposed for the future to protect the biodiversity of this intertidal area of high heritage interest.

Short-term impact of bait digging on intertidal macrobenthic assemblages of two south Iberian Atlantic systems

The present study aimed to assess short-term effects of intertidal bait digging on macrobenthic assemblages of two south Iberian Atlantic coastal systems: the Ria Formosa (RF) lagoon and the Bay of Cádiz (BC). Within each system, two different areas were selected. In each area, six plots were randomly located at least 1 m apart from each other. Half of the plots were left undisturbed (control) and the other three were dug (disturbed). Three macrobenthic core samples were taken from each plot, immediately before, one, four and seven days after digging. Samples for analyses of grain-size and organic matter content (OM) were also collected from the top 2 cm sediment layers in each sampling period. The effects of bait digging were site specific and were related to sediment and biological composition of the areas before disturbance. Macrobenthic assemblages from the area with proportionally less mud content (RF1), which presented the greatest infaunal diversity and evenness values before disturbance, showed minor effects of digging and assemblages generally recovered within 7 days. On the other hand, the areas located in the Bay of Cádiz, which before disturbance presented the greatest mud content and macrobenthic assemblages dominated by only a few species, were the most affected and did not show signs of total recovery within 7 days after digging. The abundance of sedentary polychaetes from families Spionidae, Capitellidae and Cirratulidae decreased after digging. In contrast, in some areas the abundance of the gastropods Bittium spp., Haminoea hydatis and Retusa truncatula increased after bait digging indicating that they are less affected by this activity. Differences were detected in the response of benthic assemblages to the same intensity, frequency and nature of disturbance between and within coastal systems. Therefore, generalizations of the effects of bait digging and in the recovery of macrobenthic assemblages in the south of Iberian Peninsula are not possible.

Estimation of the Diopatra neapolitana annual harvest resulting from digging activity in Canal de Mira, Ria de Aveiro

Bait digging for recreational and commercial fishing is widely practiced and economically significant. Since polychaetes often form part of the diets of several demersal species they are commonly used as fresh bait by sports and professional fishermen. The objectives of this paper are to quantify the annual bait digging of harvest Diopatra neapolitana in the intertidal mudflats of Canal de Mira, Ria de Aveiro, Portugal and comment briefly on its significance for management. Annual harvest, defined as D. neapolitana (kg) caught by collectors, was calculated as the product of independent estimates of harvesting effort using a progressive count and harvest rate through an access survey. Harvesting effort was higher during spring tides in all seasons except in winter and harvest rate lower during winter, regardless of tidal range, and higher during spring tides. Bait collection in the Canal de Mira is very intense with an annual harvest in excess of 45,000 kg per year valued at over € 325,000 per year. Management of the remove needs to take account of both the ecosystem impacts of bait digging and the socio-economic importance of bait digging to the many families involved.

Management of the exploitation of the lugworm Arenicola marina and the ragworm Nereis virens (Polychaeta) in conservation areas

Abstract In Europe, bait supply to anglers from the natural environment involves: (i) bait collection by anglers for own use, (ii) local semi‐professional bait digging and (iii) professional bait digging contracted to distributors. The management of bait digging activity is particularly acute where there is a conflict with conservation interests. Two case studies are presented describing the population dynamics of: I Arenicola marina in the Lindisfarne nature reserve, and II Nereis virens in the Menai Strait; both in conservation areas. Case I. Populations of A marina are subject to marked annual cycles in number and fresh weight. This case illustrates the response of the population to substantial overexploitation leading to a population crash. With the introduction of restrictive legislation the population was re‐established by recruitment of adults from neighbouring unexploited populations. Case II illustrates the dynamics of a N. virens population dominated by large old individuals; it does not represent a sustainable resource in contrast with populations of the same species in other locations. The management of the exploitation of bait populations in conservation areas is discussed in relation to world patterns of utilization and supply.

Effects of mechanical and manual harvesting of lugworms Arenicola marina L. on the benthic fauna of tidal flats in the Dutch Wadden sea

Abstract Effects of bait digging by hand and mechanical harvesting of Arenicola marina (L.) on the macrobenthic fauna of the Dutch Wadden Sea were investigated. Samples were taken on two tidal flat areas: the Balgzand and the Vlakte van Kerken, from March to October 1981. Most of the major species were severely reduced immediately after digging. Some species, e.g. Macoma baltica and Scoloplos armiger , showed a fast return into the depopulated area. Further recovery varied per species, with in general a larger recruitment of juveniles in the dug-over areas compared to the nondistributed areas. Mechanical harvesting appeared to be more efficient, catching more Arenicola per m 2 . Hand diggers caused less mortality of other benthic animals per gram Arenicola harvested. Disturbance of feeding birds is discussed. People walking and hand diggers cause a serious problem. The most frequently used tidal flats, within walking distance from the shore, can be more or less permanently unsuitable for feeding birds.

Distribution and population recovery of Arenicola marina and other benthic fauna after bait digging

Distribution and population recovery of Arenicola marina and other benthic fauna after bait digging

The effects of mechanical and manual digging for lugworms (Arenicola marina L.) on the benthic fauna of the tidal flats in the Dutch Wadden Sea

Effects of manual bait digging and mechanical cropping ofArenicola marina (L.) on the macrobenthic animals in the Dutch Wadden Sea were investigated. Samples were taken on two tidal flat areas: the Balgzand and the Vlakte van Kerken, from March to November 1981. Only the impacts on major species and on the total biomass are discussed.

The Influence of Bait Digging on Cockle, Cerastoderma edule, Populations in North Norfolk

The population of cockles Cerastoderma (= Cardium) eduke (L.) declined drastically in the late 1950s and '60s concurrent with intensification of digging for lug and rag worms. At Blakeney Point, where bait digging is slight, cockles remained common. A field experiment showed that digging caused heavy mortality of cockles and probably acted more severely on smaller ones of each age group. Laboratory experiments confirmed that few cockles buried at 10 cm could regain their near surface positions and that many died. Predator exclusion did not affect cockle numbers.