How Marine Reserves Can Help Preserve Ecosystems by Reducing Bycatch

By Jess Daly, SRC Intern

One of the greatest environmental impacts of industrial fisheries is the accidental removal of species in bycatch. Many fisheries have a single target species that they look to catch when they fish. Any other species that pull up in their nets or on their lines are known as bycatch. These fish are often simply discarded since the fisherman will not make money off them, even though they may be of great importance to the ecosystem. Bottom trawling is one type of fishing that involves dropping weighted nets to the bottom of the ocean and dragging them along the sea floor. Nearly 23% of fisheries use trawl nets as their primary fishing method, which is criticized both for its very high bycatch percentage (anything on or near the bottom will be pulled up in the net) as well as the destruction of corals colonies from the weights being dragged across them (Van Denderen et al, 2016). Other kinds of fishing nets, such as midwater trawls and driftnets, also typically have high bycatch percentages.

Figure 1: This illustration shows what a bottom trawl fishing net looks like as well as how it works. Source: Mr. Bijou, Blogspot

Bycatch is a serious problem, but not one that is easy to solve because of limitations of fishing equipment and the inherent difficulty of trying to fish for a single species. Traditional methods of reducing bycatch, such as limiting the total number of fish that can be taken, can be difficult to enforce and are economically costly for the fisherman (Hastings et al, 2017). Using specialized fishing gear is a second potential method, but can also be quite expensive and is not always effective. Recently, the concept of using marine reserves as a tool to help reduce bycatch has begun to gather interest. Marine reserves are areas that are designated “no-take,” meaning that nothing can be removed from the area. Fishing, bottom trawling, and taking of shells are among the activities that are not allowed inside the reserve. They are usually areas that are of great importance to fish species for a specific reason, such as a mating grounds or nursery. It has been shown in multiple studies that marine reserves cause increases in fish populations and can help depleted species to recover their numbers (Mumby and Harborne, 2011). Large female fish are exactly the type that fisherman hope to catch, so without protection they are fished out quickly and the population declines because they are not reproducing. Inside a no-take area, however, female fish can grow larger and thus produce larger, healthier offspring. The population increases and eventually flourishes, maintaining the health of the ecosystem and the fisheries’ profits simultaneously.

Figure 2: The waters off Anacapa Island, California are one example of a marine reserve, or “no-take zone”. The map shows the reserve area in red. Source: Matt Holly, National Parks Service

In some fisheries the primary bycatch species, also known as the weak stock, are slow to mature, have long lifespans, and produce fewer offspring than target species. Some fishing practices intended to maximize target species catch may decimate the weak stock and wreak ecological havoc (Hastings et al, 2017). A 2017 study conducted by Drs. Hastings, Gaines, and Costello used extensive mathematical modeling to examine the potential effects of marine reserves on fisheries. They found that in every case where the weak stock was a species with a longer life expectancy and lower reproduction rate than the target species, marine reserves increased target species yield more than other management methods. They also showed that creating no-take zones specifically designed to protect bycatch species did not decrease the maximum yield of the target species (Hastings et al, 2017).

In the first case the marine reserves increase target species yield because there is no limit on specific catch numbers, and also because they protect areas of great importance to the fish. If this area is a breeding ground or nursery, this protection results in more offspring being produced and then going on to survive to adulthood. If there are more fish in the water, more of them can be caught without damaging the population or the ecosystem. In the second case, where the marine reserve is specifically tailored to protect the bycatch species, the target species catch does not decrease significantly because the fish share a habitat. Even if the protected area is not of special importance to the target species, the fish still live in that area. If they cannot be caught inside the reserve, their numbers can increase and are able to offset extra fish that might be taken from outside the reserve.

While it may seem that completely prohibiting fishing in high-production areas would lead to decreases in fisheries profits, there is strong evidence that marine reserves effectively and cost-efficiently maintain profit margins while mitigating the economical damage of many fishing practices. By protecting bycatch species and limiting the number of unwanted fish that are removed from the ocean, ecosystems can better withstand fishing pressures and better recover from past overfishing trauma.

Works Cited

Hastings, Alan, et al. “Marine Reserves Solve an Important Bycatch Problem in Fisheries.” Proceesings of the National Academy of Sciences of the United States of America, vol. 114, no. 34, 22 Aug. 2017, pp. 8927–8934,

Mumby, Peter J., and Alastair R. Harborne. “Marine Reserves Enhance the Recovery of Corals on Caribbean Reefs.” PLOS ONE, Public Library of Science, 11 Jan. 2010,

Van Denderen, Pieter Daniël, et al. “Using Marine Reserves to Manage Impact of Bottom Trawl Fisheries Requires Consideration of Benthic Food-Web Interactions.” Ecological Applications, vol. 26, no. 7, 2 Sept. 2016,

Holly, Matt. “Anacapa Island Map.” Wikimedia Commons, National Parks Service, 25 Feb. 2016,

“Mr. Bijou”. “How Bottom Trawling Works.” Oceans Become Deserts, Blogspot, 10 Jan. 2006,

Marine Reserves Still Beneficial for Conservation Near Coastal Rivers and Cities

By Kevin Reagan, SRC Intern

As the ocean becomes more of a “hot topic” in the media and public forums, planners and designers of marine reserves must increasingly factor in socio-economic factors alongside biological principles when discussing policy. The human aspect that is usually responsible for the initial need for conservation and things like no-take marine reserves is undeniable, and as populations continue to increase, the negative impact many human activities have on marine environments does as well. These effects are particularly strong in coastal cities or estuarine flows, where a river flows into the ocean. However, this may not necessarily mean that marine reserves would not be beneficial in these areas though. In his 2015 study, Chantal M. Huijbers and colleagues analyzed whether being located close to major influences like cities on the coast affected the efficacy of marine reserves in enhancing the number of organisms that were present, relative to other areas outside of the reserve.

Diagram representing the 3 major categories of determinants expected to influence the performance of marine reserves.

Diagram representing the 3 major categories of determinants expected to influence the performance of marine reserves.

Marine reserves are usually placed in deeper, offshore locations that have little to no commercial value. These areas are generally remote, and partly chosen because they offer the least chance of the reserve interfering with human activities such as fishing. Though this leaves areas near coastal cities poorly protected, these decisions are made because of impacts like habitat degradation and fishery overexploitation that occur in coastal areas that increase pressure on marine ecosystems. Native marine diversity has been shown to decrease with increasing human population density, and coastal areas generally have greater levels of biodiversity than offshore areas; marine reserves can play a crucial role in protecting this diversity, but both positive and negative impacts have been seen. There is, though, a chance that the extent of positive effects from things like fishing restraints is overshadowed by negative effects from sources outside of the boundary of the reserve.

Edgar et al. demonstrated that for a marine reserve to be effective, it must be four out of these five things:

  • No-take zone
  • Large
  • Have high levels of compliance with regulations,
  • Have been protected for a long period of time
  • Separated from fished areas by geographic boundaries or channels

These factors demonstrate the importance of human-related factors in planning future marine reserves, and intuitively it would seem that the best framework for planning marine reserves is the current one that delegates them to remote offshore locations. But, after compiling a database of peer-reviewed studies that reported the biological effects of marine reserves and examining 150 articles published between 1977-2012 and included 113 different reserves, Huijbers found that there was a greater abundance of organisms in marine reserves compared to control areas regardless of the reserves proximity to coastal influence. Essentially, the reserves close to urban centers were indistinguishable from those that were more remote.

Example of what a healthy, protected reef can look like. Flynn’s Reef, Phillips Island, Australia, part of the Great Barrier Reef Marine Park.

Example of what a healthy, protected reef can look like. Flynn’s Reef, Phillips Island, Australia, part of the Great Barrier Reef Marine Park.

Huijber et al. only included studies that measure fish, invertebrate, and algal abundance in formally designated reserves that were also fully protect no-take areas, and each study included one or multiple sites that were both in and outside the reserve, or before/after the reserve was established. After using statistical analysis to examine the relationship between eleven predictor variables that measure the effect of coastal influence and marine reserves, they showed that coastal marine reserves were equally as effective as less-developed offshore locations. Though variations in the methodologies of the studies included in the analysis may affect the strength of the findings, the data examined and presented is compelling and at the very least warrants further research on the subject.

For any of these policies to work, efficient enforcement of rules and regulations is paramount. Planners cannot assume that people will comply with regulations out of the goodness of their hearts. Enforcement is key and studies have shown that there is a greater effect of reserves on ecosystem health and biomass where there is less encroachment. That being said, placing marine reserves near coastal areas will also raise awareness of biodiversity and can potentially increase the success of marine reserves. Coastal marine reserves can provide the crucial link between the social and ecological environments in these areas and end up fostering a sense of admiration and appreciation for what the ocean has to offer for generations to come.


Huijbers, Chantal M., et al. “Conservation benefits of marine reserves are undiminished near coastal rivers and cities.” Conservation Letters (2014).

Evolution of Motherhood: The Importance of Mature Female Fish

By Daniela Ferraro, RJD Intern

Older, female fish are becoming a necessity for the continuation of trophy-fish hunting and sustainable commercial fishing. Looking at both freshwater and saltwater species, the presence of larger, more mature fish increases the productivity and stability of fish populations. Dr. Mark Hixon, of the University of Hawai’i at Manoa, refers to the loss of big fish as “size and age truncation.” Big, old, fat, fertile, female fish, affectionately nicknamed BOFFFFs, have proved the ability to produce significantly more eggs than younger fish. They also can spawn at different times and places, allowing them the option of evading potential predators and threats to their offspring. Efforts to protect older, larger fish include creation of marine reserves, which act as no-take zones. Marine reserves allow fish to spawn throughout their entire lives. As large fish, BOFFFFs are a valuable commodity in commercial fishing, as fisheries tend to target marketable commodities. This specified targeting alters a fishery’s modes and methods: through the narrowing of mesh size or gear type. Drift nets and long lines are used in the removal of larger fish from certain populations. To some extent, even bait type and hook affects the type of fish caught. Slot limits are placed on commercial fisheries, limiting them to catching only medium-sized fish. Although egg size variation among a single species may be narrow, across a diverse range, significant maternal effects have been noted in terms of larger egg size.

BOFFFFs: Big (1.1m), old (ca.100 years), fat (27.2 kg), fertile female fish: Shortraker rockfish (Sebastes borealis). Image Source: Karna McKinney, Alaska Fisheries Science Center, NOAA Fisheries Service

BOFFFFs: Big (1.1m), old (ca.100 years), fat (27.2 kg), fertile female fish: Shortraker rockfish (Sebastes borealis). Image Source: Karna McKinney, Alaska Fisheries Science Center, NOAA Fisheries Service

More mature females produce more, and often larger, eggs that typically develop into larvae that can withstand more intense challenges like starvation and have a faster growth rate. This is partly due to the physical body size, as a larger fish translates to a wider body cavity to allow for the development of larger ovaries. BOFFFFs have a tendency towards earlier and longer spawning seasons. With this flexibility, these fish can withhold spawning in unfavorable conditions. Once the danger of predation, or other threats, has passed, BOFFFFs can spawn abundantly and improve recruitment. Hixon refers to this phenomenon as the storage effect. This ability is preferential when considering commercial and differential fishing. The targeted removal of BOFFFFs results in a truncation of size and age structure of a specific population. The removal of older fish from an overfished population will increase their probability of species collapse. The assumption that younger female fish contribute equally to production and stock is detrimental to the future of sustainable fishery stocks.

Fishery productivity would find stability in the implementation of old-growth age structures. Berkeley suggested three methods to limit the overfishing of BOFFFFs: slot size limits with both minimums and maximums, low rates of fishing mortality, and marine reserves.  This can be accomplished with enforcement of both marine reserve no-take zones as well as catch limits. Marine reserves act not only as a direct safe place for fish to thrive and procreate, but also as a healthy influence on surrounding waters. They give maturing fish an area to develop, spawn and seed nearby fisheries.

Cape Rodney-Okakari Point, Goat Island Marine Reserve, New Zealand. Image Source: Wikimedia Commons

Cape Rodney-Okakari Point, Goat Island Marine Reserve, New Zealand. Image Source: Wikimedia Commons

Marine reserves act to provide ecosystems and environments for fish to not only reach sexual maturity, but past that. In addition, larvae from healthy marine reserves are found to seed the areas directly adjacent. This will assist in the replenishment of overfished and exploited populations. By integrating large-scale marine reserves, it is believed that it is possible to halt and reverse the decline of global fisheries while also protecting marine teleost, mammal, and invertebrate species. The decrease in mortality due to the protection of species by marine reserves and the subsequent increase in productivity has been seen in both temperate and tropical locations. Since marine reserves are located along reefs, estuaries, and kelp beds, it provides a large range in the protection of a diversity of species.

In a study conducted by Steven Berkeley et al, featuring 20 female black rockfish (Sebastes melanops), from five to seventeen years, it was found that larval groups from the older females grew three times faster than their counterparts. Larvae from the older fish also survived starvation twice as long. According to Berkeley, this is due to the provision of larvae with energy-rich triaglycerol (TAG) lipids as they increase in age. The TAG volume found in oil globules is positively correlated with age, growth rate, and survival. However, maternal effects can’t be classified as consistent across every species of teleost fish. Instead, research indicates that maternal effects have developed across a diverse taxonomic range. With the removal of matured female fish, populations are more likely to develop damaging consequences in terms of biodiversity and productivity.



Berkeley, Steven A., Mark A. Hixon, Ralph J. Larson, and Milton S. Love. “Fisheries Sustainability via Protection of Age Structure and Spatial Distribution of Fish Populations.” Fisheries 85.5: 23-32. Print.

Gell, Fiona R., and Callum M. Roberts. “Benefits beyond Boundaries: The Fishery Effects of Marine Reserves.” Trends in Ecology & Evolution 18.9: 448-55. Print.

Hixon, M. A., Johnson, D.W., and Sogard, S. M. BOFFFFs: on the importance of conserving old-growth age structure in fishery populations. – ICES Journal of Marine Science, 71: 2171–2185.

Improving Marine Reserves

By Mary Trainor,
Marine conservation student

It is a wonderful sign of the times that governments around the world are taking action to protect the ocean.  One popular marine management tool is the marine protected area (MPA), which aims to conserve marine life and habitats by restricting what people can do within designated MPA boundaries (National Ocean Service 2012b).  There have recently been advancements in both the placement and abundance of state government regulated MPAs in United States waters.  For instance, in June of 2012,  the California Fish and Game Commission approved plans to implement the final 19 MPAs needed to complete the open-coast section of California’s Marine Life Protection Act, boosting California’s total MPA count to 119 (California Dept. of Fish and Game 2012).  In addition, the Florida Keys National Marine Sanctuary Advisory Council is currently re-evaluating the sanctuary’s boundaries and regulations in order to reflect changes in laws and scientific literature (National Ocean Service 2012a).

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Are Marine Protected Areas Effective?

By Natalie Torkelson,
Marine conservation student

Living in South Florida, most people are familiar with the concept of Marine Protected Areas (MPAs). The Florida Keys National Marine Sanctuary is just one of these protected areas in Florida. Six percent of the sanctuary consists of fully protected zones. Along with the fully protected zones, 27 management areas were designated when the sanctuary was created, and the sanctuary also includes 20 existing management areas that have been designated by other agencies (National Marine Protected Areas of the United States). Biodiversity, or the amount of different species in an area, is often used as an indicator of what areas are important and should be protected (Chapin et al., 2000). However, there is much evidence that there are other factors that should be taken into account when making decisions about what areas should be conserved. Many ecosystems depend more on functional diversity to remain healthy and productive than on the number of different species that it has (Nystrom 2006). Functional diversity is the number of different biological functions or processes in an ecosystem, and this, as well as trophic levels can be used to compare the communities in different areas. Measuring each of these things can help determine what areas are important to conserve, but are marine protected areas really effective? One study in the Mediterranean set out to answer this question by comparing the species, trophic, and functional diversity of protected and non-protected areas. The hypothesis was that species, trophic, and functional diversity were higher in protected areas than in adjacent non-protected areas (Villamor and Mikel 2012).

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