Image: CNP / FIS

Why is ichthyoplankton studied?

ECUADOR
Monday, April 03, 2023, 02:00 (GMT + 9)

Since the beginning of the 20th century, the first scientific investigations carried out on marine fish populations (Hjort, 1914) recognized that the dynamics of fish populations at different ages is established during the first days of life of the species. This precedent has remained unchanged ever since and gave impetus to numerous investigations of marine fish populations in relation to the dynamics of their early developmental stages (Legget & Deblois, 1994).

Poto: CNP

Fish eggs and larvae or also called ichthyoplankton are the spawning product associated with the reproductive activity of adult fish. Inside the eggs, the embryos develop until the egg hatches and the larvae emerge. They initially live adrift, floating in the sea with weak movements, unable to counteract the movement of sea currents, until through their growth they begin to develop autonomy of movement, thus allowing them to move towards areas where they can survive.

Egg and larvae monitoring

The monitoring of the abundance of fish eggs and larvae, in relation to the factors that condition their survival, becomes an annexed sample that serves to know the state of the future population with fishing interest.

This knowledge has a high social value, for example, providing information on a) spawning times and areas, b) maximum reproduction time of adult fish, c) estimation of future catches associated with larval abundance and d) evaluation of the fishery resources in general, providing information on exploited and unexploited species (Ahlstrom and Moser, 1976).

Source: CNP

Business support

From its beginning, the project has had the logistical support of the companies associated with the FIP and their crews, since on board their boats it has been collected monthly by means of vertical trawls of 70 m depth towards the surface with bongo nets, ichthyoplankton samples at nine stations located outside 8 nautical miles along the coast from Manabí to the Gulf of Guayaquil

Results achieved

The monthly monitoring carried out from September 2021 to September 2022 has recorded that the areas with the highest concentration of small pelagic eggs continue to be located in Puerto Hualtaco, Engabao, Puerto López and Salango; and the areas of larval abundance, which is related to sites where there would be favorable breeding for pre-recruitment, were located in Bajo Copé, Puntilla de Santa Elena, Anconcito and Engabao.

These findings are consistent with what has already been determined in the investigations carried out by IPIAP (Romero et al., 2018; Calderón and Ayora, 2021), being relevant for the characterization of the breeding and breeding areas of small pelagics.

Source: CNP

On a temporal scale, it was possible to characterize the period that concentrated the highest percentage of effective spawning of small pelagic adult individuals.

The spawning of the mackerel (Scomber japonicus), bottle (Auxis spp,), pinchagua (Opisthonema spp) and round sardine (Etrumeus acumunatus) species occurred between November and March, with maximums between January and February (Figure 3), results similar to what was reported by Ipiap researchers (Jurado et. al, 2016; INP, 2020). Being able to estimate that at least during the monitoring year, the spawning of small pelagics continues to occur during the wet season.

The association of oceanographic variables, such as temperatures, salinity, dissolved oxygen, with the distribution of organisms in the marine environment, allows us to understand what oceanographic parameters or processes determine the composition, distribution, and abundance of ichthyoplankton. This type of analysis made it possible to identify that the spawning of mackerel, round sardines, bottle sardines, and jabs, at least during the monitoring period, occurred in areas with average surface temperatures of 24 ˚C to 27 ˚C; while pre-recruits (older larvae with characteristics similar to juveniles) were associated with a higher concentration of dissolved oxygen (DO), chlorophyll-a (Cl-a) and zooplankton volume (VZ). This allows us to infer that in addition to parameters such as temperature, food availability plays a fundamental role for optimal larval development and survival, which will be reflected in the incorporation of juvenile fish into the adult population.

Source: CNP

Future challenges

The monitoring and follow-up carried out during the period characterized by environmental conditions typical of the La Niña phenomenon (Ormaza, 2022) has supplemented the knowledge already determined by Ipiap, about where, when and in what environmental conditions small pelagics carry out their reproductive activity. However, it is necessary to continue the sampling in environmental conditions different from those registered during September 2021 - September 2022, taking into consideration that small pelagic species are sensitive to environmental changes and fishing pressure, for which it is likely that there are monthly variations in abundance under conditions other than those sampled.

Monitoring in the medium term will allow us to continue characterizing the behavior of these species in different environmental scenarios and thereby contribute more information to the design and adoption of fisheries management measures, and even to better planning or forecasting of the development of the activity in a fishing season.

Source: Cámara de Pesquería Ecuador

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