Monitoring concepts in protected areas: habitat use and migration patterns of bony fish, sharks and rays (NIKOFIN)

Background and Objective

The preservation of biodiversity is an important conservation goal at national and international level. However, this requires in-depth knowledge of species diversity. Especially with regard to non-commercially exploited fish species, such knowledge is often only rudimentary.

Comprehensive monitoring programs to record the entire fish communities in various habitats of the North Sea do not exist and are difficult to implement for various reasons. On the one hand, for the obvious reason that fish and cartilaginous fish, unlike birds or marine mammals, are not visible at the water surface, and on the other hand, because they have a much wider range of species and inhabit a large number of different habitats - in some cases, however, often only temporarily. A single approach to the cross-habitat recording and assessment of the entire fish fauna is not feasible - different methods must therefore be combined to achieve this goal.

Traditional methods such as the use of trawls - usually bottom trawls - which have been standardized for sampling commercially relevant fish species in the North Sea to date, are ruled out since they are highly invasive, particularly in sensitive habitats and protected areas, and often also cannot be used in such areas due to the risk of damage or even loss of the fishing gear. Alternative sampling methods in such areas are passive fishing gear such as multi-mesh nets/set nets and fish traps. Fish traps in particular are considered to be significantly less invasive, as the fish caught can usually be released alive. However, it should be borne in mind that both types of fishing gear have different selectivities for different fish species and therefore may not provide a complete picture of fish diversity in the area.

The focus in the development of alternative monitoring strategies is increasingly shifting to non-invasive approaches, particularly in relation to protected areas and endangered species. Genetic methods such as environmental DNA (eDNA) and imaging methods (underwater video cameras) are particularly promising in this regard. In addition, individual fish can be marked minimally invasively with acoustic or satellite transmitters in order to identify their habitat use, preferred habitats and possible migratory movements. These methods are also subject to limitations - but a combination of several of these methods seems promising for a suitable monitoring concept in protected areas or in areas otherwise inaccessible by standard methods.

Target Group

Science, Policy (Fisheries Conservation)

Approach

In the “Habitat use” work package, reef-associated bony fish and cartilaginous fish will be tagged using acoustic telemetry and satellite tags. The stationary, reef-associated bony fish species to be tagged with acoustic transmitters are Goldsinny Wrasse (Ctenolabrus rupestris), Ballan Wrasse (Labrus bergylta) and Red Gurnard (Chelidonichthys lucerna). Among the cartilaginous fish, Tope (Galeorhinus galeus) - as a highly migratory species - and Thornback Rays (Raja clavata) - as a potentially more localized species - are also to be tagged with acoustic transmitters. Satellite pop-up tags, i.e. satellite transmitters will additionally be deployed on tope. Ideally, representatives of migratory bony fish species such as Twaite Shad (Alosa fallax) or Allis Shad (Alosa alosa) should also be tagged. The acoustic transmitters are implanted into the abdominal cavity of the fish in a short, minimally invasive procedure. The satellite transmitters are attached externally to the dorsal fin.

A network of receivers will be installed in three areas of the German North Sea and connected to the “European Tracking Network” (ETN) in order to record the small-scale movements of the tagged fish in the habitat and the use of the respective habitats (using acoustic telemetry): Sylt Outer Reef, Steingrund (near Helgoland), MarGate experimental field (Helgoland). Long-range migratory movements of tope, which temporarily aggregate in the study area, will be analyzed through measurements with satellite archival tags.

The data recorded will be used to determine the role of the respective habitats for the selected fish and cartilaginous fish species, and how these habitats are (temporarily) used by the respective species. In addition to supplementing our still limited knowledge on distribution, abundance and habitat use of these species - i.e. biological parameters - the results of the analyses should also help to develop a comprehensive monitoring concept for such species in protected areas.

Data and Methods

In the acoustic telemetry study, so-called acoustic transmitters will be used, which -depending on the configuration- allow long-term measurements over several years. For tagging, fish are caught in the respective study areas using passive methods (baited fish traps) or by angling. Selected fish are anaesthetized, and the acoustic transmitters are implanted in the abdominal cavity by means of a minimally invasive surgical procedure. After the fish have spent some time in a recovery tank and their condition has been monitored, they are released. From this point onwards, the implanted transmitters send signals at predetermined intervals.

In order to record these signals, a receiver network must be installed. In the area of the southern North Sea, a network has been established via various other international projects through the “European Tracking Network” (ETN). In the German part of the North Sea, this has yet to be implemented. We plan to deploy receivers on the Steingrund near Helgoland (known as temporary habitat of tope, important habitat for wrasse), in the MarGate underwater test site on Helgoland and on the Sylt Outer Reef (important habitat for all fish species to be studied). The receivers have a battery life of more than one year and are deployed, read out and maintained as part of the monitoring activities.

If a fish tagged with a transmitter is in the reception range of a receiver, the coded signals are recorded. This data can then be used to determine the small-scale movements within the habitat, habitat use and any periodic cycles. Animals that leave the detection range of the receiver network installed in the above-mentioned areas can still be detected if they enter the detection range of another ETN receiver. The possibility of using the ETN infrastructure therefore also allows conclusions on habitat use and regional migrations if the marked animals leave our “own” measuring field.

To record long-range migratory movements, tope - known for such migrations – will additionally be tagged with pop-up satellite archival tags. These tags record environmental parameters such as temperature, depth and light intensity over a pre-programmed period of up to 365 days. At the end of the deployment, the transmitter detaches from the shark and surfaces. There, the archived data is transmitted via ARGOS satellites (=Advanced Research and Global Observation Satellite). From this data, movement patterns, activity cycles and migration routes of the sharks can be reconstructed from the point of tagging until the transmitter detaches.

Our Research Questions

In addition to many other research questions in the joint project, our work package “Habitat use” focuses on the following questions, among others:

• Which (long-term) monitoring concept is suitable for non-commercial fish species, especially in protected areas in the North Sea?
• How can established methods for recording habitat use and migration be integrated and further developed in such a monitoring concept?
• How can the effectiveness of measures in protected areas of the German EEZ (ExclusiveEconomic Zone) be evaluated in relation to the fish species studied?
• Can we recognize/evaluate the influence of fishing exclusion zones in the protected areas on non-commercially exploited fish species or cartilaginous fish?