What Does a Fisheries Biologist Do?

Basic biological mechanism of population changes of fish and other economic aquatic organisms. The research on the basis of fishery biology can provide theoretical basis for fishery resource assessment, fishery forecast, resource management and proliferation. Its content mainly includes five aspects of population, reproduction and development, feeding and growth, population structure and death, and inter-species relations. Among them, the study of population and its structure is the most important. The basic unit of the following categories of population, a natural combination of individuals with very similar morphological characteristics and ecological and physiological characteristics. Individuals in the population can mate and reproduce freely. Stocks are also a unit of measure for fishery resources. Scientifically dividing populations is a prerequisite for conducting qualitative and quantitative research on resources.

Fishery biology basis

A basic unit of the following classification, a natural combination of individuals with very similar morphological characteristics and ecological and physiological characteristics. Individuals in the population can mate and reproduce freely. Stocks are also a unit of measure for fishery resources. Scientifically dividing populations is a prerequisite for conducting qualitative and quantitative research on resources.

Due to geographical isolation, a population often has its own specific living and migratory distribution areas, as well as a unique law of quantitative changes. Due to breeding segregation, sometimes different ecological populations will appear in the same living distribution area. Due to the differences in the characteristics of fish activities, the degree of environmental isolation, and the status of water exchange, the populations of fish are also very different. Bottom fishes distributed in shallow coastal waters have a limited range of activity, and a species can often be divided into many populations. Some oceanic pelagic fishes and eels have a small number of populations due to their long migration distance. European eels, such as those distributed in North Africa, the Mediterranean coast, and Norway's inland waters, all come from algae, so there is only one population.

In the late 19th century, German and Danish extensive studies of fishes off the coasts of Northern Europe and North Atlantic were conducted. They found that there were differences in the measurement characteristics (frequency distribution, average value) of the shoal fish in each part of the sea area, or the number of vertebrae, fins, and other counting characteristics. When judging whether the fishes caught in the two places belong to different populations by using measurement or counting features, some scholars have proposed that there must be a difference of 3/4 items to be judged as different populations, which is the so-called 75% rule. However, other scholars believe that if there is a stable difference between the frequency distribution of the counting features and the average, even if there is only one counting feature, it can be directly judged as a different population. In fact, it is also common for the count items to be measured to have little or no variation. Ecological methods are often used in combination with fish populations to determine biological characteristics. Such as measuring the scale characteristics of fish scales and otoliths, the growth curve of fish schools and the parasitic conditions of parasites. Biochemical methods can also be used to divide fish populations. Commonly used are serum agglutination reactions. When the antiserum is dripped into the fish protein that originally produced the antigen, the more closely related blood will produce more turbid sediments. The further the blood relationship is, the less the precipitation will be. The molecular biology methods often used in recent years are based on the differences in protein charge mobility of different species of fish. Specific methods include sarcoplasmic protein electrophoresis, hemoglobin electrophoresis, and various isoenzyme electrophoresis.

Fish populations that are relatively stably distributed in a certain water area often have certain age, body length, weight and male-to-male ratio structures. By measuring these structures, a conversion table of length and age can be made, and then based on the relationship between body length and weight Curves and body length data and total yield data of large quantities of catches are used to convert the total number of catches and weights of fish of all ages that reflect the status of the population. If the fishing effort in the next two years is similar, comparing the total catches of the two adjacent age groups in the two years before and after, the total survival and death of the middle and advanced age groups can be roughly estimated.

The total mortality of undeveloped populations is equal to the natural mortality, so the natural age of the population can be estimated from the maximum age and its tails that appear in a certain number of sampling tails (see the logarithm of fish sampling tails and total mortality relationship]). Based on the highly developed total mortality rate, the total fishing mortality rate and the total amount of resources can be estimated. The natural mortality of fish is extremely stable, except for the early stages of development, which are fairly stable in subsequent years.

After the development of a population, as the fishing mortality rate gradually increases, its natural mortality rate gradually decreases accordingly. However, the population itself has the ability to adjust and adapt. For some long-lived and resource-rich fish species, due to the small proportion of pre-development catches in resources, and the effect of fishing on long-lived fish species is greater than that of annual animals. Slow, so its total mortality tends to remain stable, with little difference from the original population. For example, the giant yellow croakers that have been developed along the coast of China have a very similar age structure to the large yellow croakers of the Lusi group when they were first developed in the early 1960s. Therefore, resources can be monitored in the early stages of development by measuring fish length or weight. However, the population structure also changes due to changes in the supplementary amount or the occurrence of strong generations, and its stability and variability depend to a large extent on the changes in the abundance of resources in each generation. For long-lived, slow-growing, and late-maturity populations, delaying the catch age often results in larger catches. The opposite is true for short-lived, fast-growing, and early-maturity populations. As long as the reproduction mechanism can be maintained normally, it is more advantageous to start the fishing early.

The inter-species relationships of various organisms in waters are very complicated. These relationships include not only competition between predators and prey, parasites and hosts, but also mutually beneficial relationships such as swarming. Due to the omnivorous nature of fish at middle and high latitudes, there is obvious food competition between fingerlings, especially at the juvenile stage. If the distribution of the two fingerlings is similar to the breeding period, the strained food relationship is often Will cause fluctuations in the population number, such as the phenomenon of mutual fluctuation between the number, which is caused by this.

During the evolution of fish, two different adaptations to the environment were formed: one is the r-selective adaptation, which is short life span, unstable population size, fast recovery, and strong anti-catch ability, or r countermeasure; The species is K-selective adaptation, or K-strategist, with long life span, stable population, slow recovery, and weak anti-capturing ability. The focus of resource protection should be K countermeasures.