Overview
The nursery habitat hypothesis states that the contribution per unit area of a nursery habitat is greater than for other habitats used by juveniles for the species. Productivity may be measured by density, survival, growth and movement to adult habitat (Beck et al. 2001).
There are two general models for the location of juvenile habitats within the total range for a species which reflect life history strategies of the species. These are the Classic Concept: Juveniles and Adults in separate habitats. Juveniles migrate to adult habitat. General Concept: overlap of juvenile and adult habitats.
Some marine species do not have juvenile habitats, e.g. arthropods and scallops. Commonly fish, ells, some lobsters, blue crabs (and so forth) do have distinct juvenile habitats, whether with or without overlap with adult habitats.
In terms of management, use of the nursery role hypothesis may be limiting as it excludes some potentially important nursery sites. In these cases the Effective Juvenile Habitat concept may be more useful. This defines a nursery as that which supplies a higher percentage of individuals to adult populations.
Identification and subsequent management of nursery habitats may be important in supporting off-shore fisheries and ensuring species survival into the future. If we are unable to preserve nursery habitats, recruitment of juveniles into adult populations may decline, reducing population numbers and compromising the survival of species for biodiversity and human harvesting.
Determination
In order to determine the nursery habitat for a species, all habitats used by juveniles must be surveyed. This may include kelp forest, seagrass, mangroves, tidal flat, mudflat, wetland, salt marsh and oyster reef. While density may be an indicator of productivity, it is suggested that alone, density does not adequately provide evidence of the role of a habitat as a nursery. Recruitment biomass from juvenile to adult population is the best measure of movement between the two habitats.
Consider also biotic, abiotic and landscape variability in the value of nursery habitats. This may be an important consideration when looking at which sites to manage and protect. Biotic factors include: structural complexity, food availability, larval settlement cues, competition, and predation. Abiotic: temperature, salinity, depth, dissolved oxygen, freshwater inflow, retention zone and disturbance. Landscape factors involve: proximity of juvenile and adult habitats, access to larvae, number of adjacent habitats, patch shape, area and fragmentation. The effects of these factors may be positive or negative depending on species and broader environmental conditions at any given time.
It may be more holistic to consider temporal variation in habitats used as nurseries, and incorporating temporal scales into any testing is important. Also consider assemblages of species. Single species approaches may not be able to be used to adequately manage systems appropriately.
Acosta and Butler conducted experimental observation of spiny lobster to determine which habitats are used as nurseries. Mangroves are used as preferred nursery habitat when coral density is low. Predation on newly settled larvae was lower in mangrove than in seagrass beds and coral crevices. In comparison, Pipefish prefer seagrass over algae and sand habitats. King George Whiting have a more complex pattern of development. Settlement is preferred in seagrass and algae. Growth stages are primarily preferred in reef algae. 4 months post settlement, they move into unvegetated habitats (Jenkins and Wheatley, 1998).
Elusive Juvenile Habitats
For many fish species, including commercially exploited species that require careful management, juvenile habitats are unknown. In these cases, identifying nursery habitats requires knowledge of the spawning behavior and larval development of the species, and knowledge of the oceanography of the local marine environment (water currents; temperature, salinity, and density gradients; etc.). In combination, these sources of information can be used to predict where eggs go after spawning, where larvae hatch, and where larvae settle and metamorphose into juveniles. Further study of these settlement locations can identify the nursery habitats that should be considered in the management and conservation of the species.
For example, pelagic broadcast spawning, one of several spawning strategies known for marine species, occurs when eggs are released into some level of the water column and left to drift among the plankton until the larvae hatch and grow large enough to settle in nursery habitats and become juveniles after metamorphosis. To identify nursery habitats of pelagic broadcast spawning species, such as halibut, cod, grouper, and others, the first step is to identify the adult spawning grounds. This can be done with targeted fishing surveys and dissection of fish gonads for maturity stage. The location of the fish with mature (i.e. ready-to-spawn) gonads can be inferred as a spawning location.
Pelagic eggs are buoyant or semi-buoyant and will be subject to the currents and gradients at the level of the water column in which they were released. Plankton surveys at different depths above the spawning grounds of a species can be used to parcel out where in the water column the eggs have been released. Data on the water currents and environmental gradients at the same depths as the pelagic eggs can be incorporated into circulation models and used to calculate likely dispersal patterns for the eggs and subsequent larvae.
Information on the duration of larval development (i.e. the number of days it takes for an individual to develop into each larval life stage) can indicate how long the species remains in the water column and the distance the species may travel once it has reached a motile life stage instead of passively drifting. The knowledge of such larval movement capability can inform the likelihood that areas represent nursery habitats.
Other relevant information for identifying elusive nursery grounds is the presence or absence of appropriate prey for settling larvae and young juveniles, the presence or absence of predators, and the preferred environmental thresholds (temperature, salinity, etc.). Habitats that do not contain the properties necessary to support a juvenile of the given species are not likely to be nursery habitats, even if models of egg and larval dispersal indicate the possibility of settlement in those areas.
The humphead wrasse is a large species of wrasse mainly found on coral reefs in the Indo-Pacific region. It is also known as the Māori wrasse, Napoleon wrasse, Napoleon fish, so mei 蘇眉 (Cantonese), mameng (Filipino), and merer in the Pohnpeian language of the Caroline Islands.
A marine reserve is a type of marine protected area (MPA). An MPA is a section of the ocean where a government has placed limits on human activity. A marine reserve is a marine protected area in which removing or destroying natural or cultural resources is prohibited, marine reserves may also be "no-take MPAs,” which strictly forbid all extractive activities, such as fishing and kelp harvesting. As of 2007 less than 1% of the world's oceans had been set aside in marine reserves. Benefits include increases in the diversity, density, biomass, body size and reproductive potential of fishery and other species within their boundaries.
The Australian bass is a small- to medium-sized species of primarily freshwater fish found in coastal rivers and streams along the east coast of Australia. A member of the genus Macquaria from the family Percichthyidae, the Australian bass is an important member of the native fish assemblages found in east coast river systems. It is a native predatory fish and an extremely popular game fish species among anglers. The species was simply called perch in most coastal rivers where it was caught until the 1960s, when the name "Australian bass" started to gain popularity.
The common galaxias or inanga is a very widespread Southern Hemisphere fish in the family Galaxiidae. It is a slim, narrow fish with a forked tail and a mottled, spotty pattern, typically about 10 cm (4 in) long when fully grown. It lives in fresh water, but spawns at river mouths and spends the first six months of its life at sea, returning en masse in spring. Its vernacular names include cowfish, jollytail, common jollytail, eel gudgeon, inaka, native trout, pulangi, puye, slippery tarki, spotted minnow, Falklands minnow and whitebait.
A fish hatchery is a place for artificial breeding, hatching, and rearing through the early life stages of animals—finfish and shellfish in particular. Hatcheries produce larval and juvenile fish, shellfish, and crustaceans, primarily to support the aquaculture industry where they are transferred to on-growing systems, such as fish farms, to reach harvest size. Some species that are commonly raised in hatcheries include Pacific oysters, shrimp, Indian prawns, salmon, tilapia and scallops.
The yellowbelly flounder is a flatfish of the genus Rhombosolea, found around New Zealand. A different species from the genus Rhombosolea is found in Australia and also goes by the name yellow-belly flounder. The Māori people have commonly fished for R. leporina, and many other species of flatfish, throughout New Zealand's coastal waters for hundreds of years. The Māori name for this species is pātiki tōtara.
The Pacific ladyfish, also known as the Pacific tenpounder and machete, is a species of ray-finned fish in the genus Elops, the only genus in the monotypic family Elopidae. The Pacific ladyfish can be found throughout the southwest U.S. and other areas in the Pacific Ocean.
The shortnose sturgeon is a small and endangered species of North American sturgeon. The earliest remains of the species are from the Late Cretaceous Period, over 70 million years ago. Shortnose sturgeons are long-lived and slow to sexually mature. Most sturgeons are anadromous bottom-feeders, which means they migrate upstream to spawn but spend most of their lives feeding in rivers, deltas and estuaries. The shortnose sturgeon is often mistaken as a juvenile Atlantic sturgeon because of its small size. Prior to 1973, U.S. commercial fishing records did not differentiate between the two species: both were reported as "common sturgeon", although it is believed based on sizes that the bulk of the catch was Atlantic sturgeon. The shortnose is distinguishable from the Atlantic sturgeon due to its shorter and rounder head.
Marine larval ecology is the study of the factors influencing dispersing larvae, which many marine invertebrates and fishes have. Marine animals with a larva typically release many larvae into the water column, where the larvae develop before metamorphosing into adults.
The giant trevally, also known as the lowly trevally, barrier trevally, ronin jack, giant kingfish, or ulua, is a species of large marine fish classified in the jack family, Carangidae. The giant trevally is distributed throughout the tropical waters of the Indo-Pacific region, with a range stretching from South Africa in the west to Hawaii in the east, including Japan in the north and Australia in the south. Two were documented in the eastern tropical Pacific in the 2010s, but whether the species will become established there remains to be seen.
The glassy sprat is a type of sprat fish. The fish, when alive, is translucent, so it gets the second word in its scientific name from the Latin word translucidus, meaning transparent, diaphanous. In animal classification the glassy sprat belongs to Osteichthyes, Clupeiformes, Clupeidae, Hyperlophus. The glassy sprat is native to Australia and mainly found in Australia. It is marked as NE because it has not yet been evaluated by the World Animal Protection. It is mainly used as an economical aquatic product. In ecosystems, they are at the bottom end of the food chain, feeding mainly on plankton, which are less aggressive and very vulnerable to other fish. Glassy sprat are tiny in size and translucent with a silvery streak that extends from its tail to just behind its head. As early as a hundred years ago, Australians harvested the glassy sprat in large quantities and it featured on the table as food for a long time. Due to its poor appearance, it is not a very good ornamental fish.
This is a glossary of terms used in fisheries, fisheries management and fisheries science.
Spawn is the eggs and sperm released or deposited into water by aquatic animals. As a verb, to spawn refers to the process of freely releasing eggs and sperm into a body of water ; the physical act is known as spawning. The vast majority of non-mammalian, non-avian and non-reptilian aquatic and/or amphibious lifeforms reproduce through this process, including the:
Coastal fish, also called inshore fish or neritic fish, inhabit the sea between the shoreline and the edge of the continental shelf. Since the continental shelf is usually less than 200 metres (660 ft) deep, it follows that pelagic coastal fish are generally epipelagic fish, inhabiting the sunlit epipelagic zone. Coastal fish can be contrasted with oceanic fish or offshore fish, which inhabit the deep seas beyond the continental shelves.
Macrostrombus costatus, formerly known as Strombus costatus and Lobatus costatus, or commonly known as the milk conch, is a species of large sea snail, a marine gastropod mollusk in the family Strombidae, the true conchs. They are an edible species and important food source for the inhabitants of where they are found. Conchs are most notable for their medium to large-sized ornamental shells. Milk conchs are dispersed among the tropical waters of the Atlantic Ocean, along the coasts and islands of North, Central, and South America.
A marine habitat is a habitat that supports marine life. Marine life depends in some way on the saltwater that is in the sea. A habitat is an ecological or environmental area inhabited by one or more living species. The marine environment supports many kinds of these habitats.
Ichthyoplankton are the eggs and larvae of fish. They are mostly found in the sunlit zone of the water column, less than 200 metres deep, which is sometimes called the epipelagic or photic zone. Ichthyoplankton are planktonic, meaning they cannot swim effectively under their own power, but must drift with the ocean currents. Fish eggs cannot swim at all, and are unambiguously planktonic. Early stage larvae swim poorly, but later stage larvae swim better and cease to be planktonic as they grow into juveniles. Fish larvae are part of the zooplankton that eat smaller plankton, while fish eggs carry their own food supply. Both eggs and larvae are themselves eaten by larger animals.
Sea cucumber stocks have been overexploited in the wild, resulting in incentives to grow them by aquaculture. Aquaculture means the sea cucumbers are farmed in contained areas where they can be cultured in a controlled manner. In China, sea cucumbers are cultured, along with prawns and some fish species, in integrated multi-trophic systems. In these systems, the sea cucumbers feed on the waste and feces from the other species. In this manner, what would otherwise be polluting byproducts from the culture of the other species become a valuable resource that is turned into a marketable product.
The Gulf flounder is a species of saltwater flounder.
Fish go through various life stages between fertilization and adulthood. The life of a fish start as spawned eggs which hatch into immotile larvae. These larval hatchlings are not yet capable of feeding themselves and carry a yolk sac which provides stored nutrition. Before the yolk sac completely disappears, the young fish must mature enough to be able to forage independently. When they have developed to the point where they are capable of feeding by themselves, the fish are called fry. When, in addition, they have developed scales and working fins, the transition to a juvenile fish is complete and it is called a fingerling, so called as they are typically about the size of human fingers. The juvenile stage lasts until the fish is fully grown, sexually mature and interacting with other adult fish.
