Mighty fish migrations are among the greatest marvels of nature. On April 21, 2018, people around the globe will celebrate World Fish Migration Day, building awareness of just how critical moving between habitats is for many species. Why spend the energy to migrate? These fish are on a quest to find suitable sites to spawn and then move back to productive habitats to feed for the rest of the year.
Migratory fishes come in all sorts of sizes, from wee minnows to giant catfish that weigh three times as much as a refrigerator! Regardless of size, many challenges arise during these marathon swims. For example, man-made barriers such as dams can stop fish in their tracks. Rivers around the world now have at least some dams, but few of them include passages to allow fish to migrate around or over them. Not even the Olympic athletes of the fish world, salmon, can overcome such obstacles.
While dams are numerous, their numbers pale in comparison to road crossings. Culvert pipes are installed where our roads pass over streams and rivers. If poorly designed or maintained, these road crossings create major challenges for navigation. In the Laurentian Great Lakes region alone, there are over 257, 000 obstacles (culverts and dams) that fish encounter in their migratory quests. When fish can’t reach ideal locations for spawning or feeding, the consequences for their population size can quickly become noticeable.
World Fish Migration Day is an opportunity to raise awareness about the threats that migratory fishes face, but I think about these challenges year-round. As a research biologist at Shedd Aquarium, I’m currently working with Dr. Pete McIntyre and other scientists from the University of Wisconsin-Madison’s Center for Limnology to discover the effects of culverts on the greatest of the spring migrations from the Great Lakes: white suckers (Catostomus commersonii) and longnose suckers (Catostomus catostomus)! Along with understanding which barriers block fish, I’m also concerned with how the timing of migrations is shifting as our climate warms. Why would it matter if the suckers show up in the streams earlier than usual? Because they fertilize the streams, boosting the growth of plants in much the same way that a gardener does by adding fertilizer to young plants. These nutrients kick-start the food web each year, boosting the growth of the bugs that become prey for stream fish, birds and bats. If the suckers show up before the algae and invertebrates are ready for their growth spurt, the productivity of the whole ecosystem could be affected.
With the help of citizen scientists who volunteer their time to record the arrival of the fish in Illinois, Wisconsin and Michigan, we are creating a first-description of the timing of the enormous sucker migrations from Lake Michigan and Lake Superior. Last year alone, our team documented the migrations of more than 26,000 fish.
We are not alone; many other scientists worldwide are investigating other aspects of fish migrations and how to help reduce the obstacles that block these spectacular animals from fulfilling their quest. Through public assistance and collaborative efforts, we can all help migratory fish get where they need to go.
By Grace Klinger, Science Communications Fellow at Shedd Aquarium
Worldwide, the seafood industry represents $362 billion in first sale value for the global economy and accounts for roughly 59.6 million jobs. Given its economic value, it is important to keep a close eye on the way the seafood industry is managed to ensure it is viable long-term. National Seafood Month, celebrated in the month of October, raises awareness about why it’s important to support sustainable and responsible fisheries (fishing industries) and how consumers can help by choosing to eat sustainable seafood.
Sustainable seafood is seafood that is harvested in ways that allow people to enjoy seafood for years to come without leaving the fish populations unrecoverable. It allows the fishing industry to flourish while keeping the aquatic habitats, which support the fishing industry, healthy. Without sustainable fishing practices, we put the delicate balance of the food webs in the world’s oceans and lakes at risk.
Global decreases in marine fish populations have a negative impact on the fishing industry. There is an estimated 31 percent of marine species that are overfished, according to a report from the Food and Agriculture Organization of the United Nations, suggesting that more sustainable management of fisheries is needed across the globe.
One example of unsustainable fishing practices that Shedd Aquarium’s marine research team studies involves catching fish during spawning, or mating, and as fish migrate to spawning sites. Harvest during these critical windows removes large numbers of fish before they can reproduce and puts the next generation at risk. The short-term gains of fishing during these times produce massive catches and financial benefits for fishers. However, long term effects include fewer fish and jobs in subsequent years for the fishing industry and – ecologically – an increase in marine animals approaching the Endangered Species List.
For example, Caribbean snapper species are important reef fishes and a valuable seafood source. Five known snapper species have at least 20 spawning aggregation sites surrounding Cuba where many thousands of fish gather to mate. Long migration routes between far-flung spawning sites create challenges to prevent snapper overfishing. One conservation management strategy involves setting up marine protected areas near the aggregation sites and along migration routes, where no fishing is allowed, although illegal fishing and large management areas make this difficult to enforce.
Our Shedd research team partnered with researchers at the Florida Institute of Technology, University of Miami and the Institute of Marine Sciences in Havana, Cuba to try to address snapper conservation. The researchers collected data to help guide management of vulnerable snapper during their migrations and spawning times by tracking spawning events and modeling the dispersal of larvae, or baby fish, after spawning.
Why track snapper larvae too?
To ensure a “stock,” or species, is fished sustainably, it is important to know where the next generation is coming from. Understanding how fish populations are connected lets us pinpoint which areas need protection based on larvae export, or dispersal, which helps replenish populations. We can also learn if the aggregation site is “self-recruited,” meaning that the larvae are not from distant areas, but rather that they come from the local stock.
Tracking spawning events is relatively predictable because they follow the cycles of the moon. Larvae dispersal, however, is much more difficult to monitor or model. This is because of the underwater current, hurricane movements and even underwater terrain that can force larvae to stay in the same area or be transported long distances.
What Shedd’s research team found, published this year inFisheries Oceanography, is that Cuban snapper larvae dispersal can widely vary depending on different sites around the island. While some sites exhibit high self-recruitment, other sites show far dispersal routes to other countries near Cuba, which help replenish those nations’ snapper populations. This means that there can be a high larvae export at many spawning sites, all the while larvae are being “imported” from other aggregation sites.
These high export/import sites suggest the need for aggregation protection. However, current local protection varies. To fulfill the inadequacies of the marine protected areas on the spawning and pre-spawning aggregation sites, the study suggested implementing seasonal no-fishing bans for these spawning marine fishes to ensure this fishery operates sustainably.
The Caribbean snapper is an example of how science can help ensure that seafood is sustainable by identifying problems and proposing solutions before a fish population disappears. Indeed, many fishery stocks have been rebuilt in recent years due, in part, to sustainable management practices and increased awareness of the problem of overfishing. That is why celebrations like National Seafood Month are so important – being part of the solution means being an informed consumer.
Monterey Bay Aquarium’s Seafood Watch app helps you stay up-to-date on fish stocks and “best choice” seafood options. Additionally, you can support sustainable fisheries by simply choosing seafood off the beaten path. Diversify your diet and try different types of seafood to decrease demand on shrimp, tuna and salmon, which make up more than 50 percent of seafood consumed in the U.S.
For more information about how you can be an educated seafood consumer, visit www.sheddaquarium.org/seafood.