For us at Havets Hus it is important to conserve the biological diversity of the ocean. One way is to work with breeding and release of endangered or protected species. 60 % of the water volume in the aquarium is used for that. Primarily we work with two species in the North sea: small spotted red sharks and thornbacked rays, but also hope for new exciting projects with cod, catfish and large spotted red sharks. In our aquarium you can observe them close up.
Small spotted red sharks
The small spotted red shark is a shark species classified as viable. It has been protected in Sweden for many years, that is to say it is forbidden to catch or land them.
At Havets Hus you will find small spotted red sharks in many public aquariums. A juvenile aquarium and two large aquariums where they swim together with other creatures. Since 2003 we have released circa 200 tagged aquarium-bred sharks into the Gullmarn fjord. Through this we are hoping to increase knowledge on small spotted red sharks’ habits and promote more sharks in our area. So far, we know where more than 20 of them went, i.e. over 10% of all we released.
Recovery
Of these, half a year after release, one had swum into the Saltkälle fjord deep inside Gullmarn, one was caught at a depth of just under 70 meters outside Mollösund, where it had swum to only a few weeks after being released, and another had, after half a year, swum all the way to Fjällbacka. One was caught right outside Gåsö outside Gullmarn and another found by the ferry inside Gullmarn. The majority of those found had entered crayfish baskets in fairly deep water and then been returned back into the sea again. Even wild untagged sharks get into crayfish baskets, probably attracted by the bait, so it seems to be natural behaviour.
In the spring of 2015 one of our sharks was found dead on Ringshaugstranda in Tønsberg municipality in Vestfold, Norway. Through the shark’s ID tag, we could see that it was released from Havets Hus in 2005 and had lived 10 years before it died. Thus, we know that this shark had been at least 14 years old as it was four years old when it was released from Havets Hus. In autumn of 2021, we recaptured one and the same shark from the sea bed outside Havets Hus on two different occasions. That our released sharks move along the Bohus coast, into Gullmarn and as far as Norway, bodes well for the genetic work done on the small spotted red shark in the North Sea.
Telemetry
However, as the recaptures were limited, it has become desirable to fit transmitters to the sharks, so-called telemetry, so that each shark can be tracked. Starting in 2021, a project was initiated where acoustic transmitters were inserted into the sharks. The transmitters sent out sound signals which were picked up by receivers placed in the Gullmarn fjord and along the Swedish west coast. The transmitters registered the position, depth, acceleration, temperature and the shark’s ID. The project is a collaboration with Havets Hus in Lysekil and researchers Gustav Hellström, Tomas Brodin, Petter Lundberg and Daniel Palm at The Department of Game, Fish and Environment at SLU in Umeå. About 40 sharks now swim around with this kind of transmitter in them and give us detailed information on their behaviour in the wild after being born and raised in an aquarium environment. The receivers will thus enable the registration of other species equipped with transmitters in future projects.
Gustav Hellström och Eva-Lotta Blom, SLU, working with the transmitters in Gullmarsfjorden.
THORNBACKED RAYS
Thornbacked rays are threatened in both Swedish and European waters. It is totally forbidden to capture or land them in Swedish waters. Their size means that they easily get fastened in trawler nets and at one year they are already big enough that they can get caught by accident. In addition to trawling, changing habitats and lack of food could possibly be responsible for the decline in thornbacked rays. Thornbacked rays, like most rays, have a hard time recovering as it takes a long time for them to reach sexual maturity, and the reproduction rate is very low. At Havets Hus we have several large thornbacked rays that lay fertilised eggs.
In January of 2016 the first thornbacked ray was born at Havets Hus and there have been many since. In summer of 2021 we released our first aquarium-bred thornbacked ray. The goal is to breed and release thornbacked rays in the same way that we did with the small spotted red sharks, and so far, it looks promising.
COD
By studying cod one knows that the mortality rate is high for the eggs and the cod up to one year. Over half of the cod that survive the first year are caught by fishing. To get large fish once again will require that both the natural wastage and volume of fishing have to be reduced.
A possible strategy to get around the natural mortality can be to collect in small fish and let them grow in a protected environment. To later release them into an area free from fishing so that they have the potential to restore the local marine environment. Which is why Havets Hus began testing this on a small scale. The small fish that are collected in, can feed well in the aquarium protected from other predators and then released again, with tags to track how things go. The larger they are the higher the survival in the wild. Of the cod that were collected in in 2018, the first were released in 2019. The same year new small fish were collected in and released the year after. All were tagged with a tracking number. The cod had then grown to circa 40 cm. Of the roughly 70 that were then released, only one recapture has been reported. The cod was caught outside Skagen three months after release.
In October 2023 nearly 60 cod were released, of which 50 had telemetry transmitters, in collaboration with the Swedish University of Agriculture SLU. The transmitters were financed by the Marie-Claire Cronstedt’s Foundation. This is the first time such advanced transmitters were used with cod in our local environment. It meant that we could track all the cod released and not just those that were reported on recovery. The transmitters also collected information on temperature, depth and activity. Soon the rest of the cod will be released. At the moment the cod project at Havets Hus is an information-gathering project, but we also hope to investigate whether breeding of small cod can be scaled up in a way that contributes to returning large cod to the ecosystem. (2036)
WOULD YOU LIKE TO JOIN US AND CONTRIBUTE TO THE CONSERVATION WORK OF HAVETS HUS?
To breed and release marine creatures is both hard and takes time and resources. When you visit the aquarium, you contribute financially to our conservation work through the payment of entrance fees to the aquarium. Another way to support us is to put money into our bank account/transfer:
Payee Havets Hus
Strandvägen 9
SE-45330 Lysekil
BIC NDEASESS
IBAN SE06 9500 0099 6034 1489 8969
It is important that you label the payment as “donation”, so that we can track and report how much has come in and what the money has been used for.