Fish resource prediction method based on change of male-female sex ratio

Abstract

The invention discloses a fish resource prediction method of female and male sex ratio change. The method comprises the following steps: constructing female and male gymnocypris przewalskii population vectors in a lake and a river of a target lake; calculating the population number of lakes and rivers every year; calculating the sex ratio of the gymnocypris przewalskii in lakes and rivers; calculating a repeated propagation coefficient; establishing a relationship between a river male-female ratio and a lake male-female ratio; and predicting the total resource quantity of the lake gymnocypris przewalskii in the future based on the relationship between the river male-female ratio and the lake male-female ratio and the repeated propagation coefficient. Based on the ecological habit of'lake inhabiting-river breeding 'of migratory fishes, accurate accounting of the population number is achieved by constructing the lake population vector and the river breeding population vector, the sex ratio feature, breeding coefficient and lake population cardinal number of the river breeding population are combined, the linkage logic of the population supplementation amount and the existing resource amount is more complete, and the breeding efficiency of the migratory fishes is improved. And the prediction error caused by data isolation is obviously reduced.

Description

Technical Field

[0001] This invention relates to the field of fishery resource assessment and ecological prediction technology, specifically to a method for predicting fish resources based on dynamic changes in the sex ratio, which is particularly suitable for anadromous fish species such as the Qinghai Lake naked carp, which have special biological characteristics. Background Technology

[0002] Qinghai Lake naked carp ( Gymnocypris przewalskii The naked carp (hereinafter referred to as "naked carp"), also known locally as "Huangyu," belongs to the genus *Gymnocypris* of the subfamily Schizothorax in the family Cyprinidae of the order Cypriniformes. It is a core species and the only dominant species in the Qinghai Lake ecosystem, and its population resources significantly influence the structure and functional stability of Qinghai Lake's unique aquatic ecosystem. The naked carp's migratory classification belongs to the anadromous spawning subtype within the river-sea migratory type. They grow and fatten in the saline environment (Qinghai Lake) and migrate upstream to freshwater rivers each breeding season to reproduce, forming a unique life history of "fatting in the lake and reproducing in the river." Assessing and predicting its population size is crucial for scientifically formulating conservation strategies and maintaining the ecological balance of Qinghai Lake.

[0003] However, traditional fish resource assessment methods (such as acoustic assessment, mark-recapture, and unit effort catch analysis) mainly focus on the total population or the size of the spawning population, often neglecting the structural parameters within the population, especially the dynamic changes in the sex ratio and its decisive impact on the population's replenishment capacity. For naked carp, this may lead to the one-sidedness of the assessment results and insufficient predictive efficacy. The reproductive biology of naked carp has the following special characteristics and vulnerabilities: (1) Reproductive intermittency: Not all adult fish participate in reproduction every year, and the effective reproductive population depends on the gonadal development status. (2) Gonadal development differences: The nutrition and time required for ovarian development in female fish are much higher than that in male fish testes, resulting in natural differences in the frequency and ability of male and female individuals to participate in reproduction. (3) Habitat sex ratio separation: There are significant differences and correlations between the sex ratios (denoted as R:1 and r:1, respectively) in lakes (feeding grounds) and rivers (spawning grounds). The sex ratio (R) in lake areas reflects the overall resource structure, while the sex ratio (r) in river channels directly determines the reproductive efficiency and fertilization success rate in the current season.

[0004] Long-term monitoring data (since 1963) indicates a persistent "imbalance" in the sex ratio of naked carp, with an excessively high proportion of females and significant differences in sex ratios across different age groups. Ecologically, a certain degree of female bias (R>1) may be normal for naked carp because males recover their gonads quickly and have shorter reproductive cycles. However, severe sex imbalance (excessively low male ratio) directly leads to insufficient individuals for effective mating during the breeding season, decreased fertilization rates, and ultimately weakens the population's replenishment potential, putting the population at risk of decline. Currently, major technical obstacles exist in systematically integrating sex ratio dynamics into resource prediction models due to limitations such as the disconnect between monitoring data and quantitative relationship transformation, the lack of resource prediction models that integrate the "lake fattening-river reproduction" life history and population structure, and delayed early warning.

[0005] It is evident that existing technologies lack a specific predictive method for naked carp and similar life-history fish species that can quantify the long-term dynamic impact of changes in the sex ratio on population resources. This makes it difficult for management departments to accurately assess structural risks, predict population development trends, and formulate forward-looking and precise conservation measures. This invention aims to provide a predictive method that couples the sex ratio in lake and river habitats, revealing how changes in the sex ratio affect reproductive efficiency and thus determine resource replenishment. This method aims to achieve more scientific and sensitive prediction and early warning of naked carp population resources, providing a key decision support tool for the high-level protection of the Qinghai Lake ecosystem. Summary of the Invention

[0006] The purpose of this invention is to address the above-mentioned shortcomings in the prior art by providing a method for predicting fish resources based on changes in the sex ratio, thereby solving the problems that the prior art is difficult to adapt to the dynamic changes in the sex ratio of fish populations and that the prediction results lack scientific validity and reliability.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for predicting fish resource changes in the sex ratio, comprising the following steps: S1. Construct the population vectors of female and male naked carp in the target lake; S2. Construct population vectors for female and male naked carp in the migratory breeding population of naked carp in the target lake's rivers; S3. Calculate the annual population size of lakes and rivers based on the population vectors of female and male fish in lakes and rivers. S4. Based on the population vectors of female and male naked carp in lakes, the population vectors of female and male naked carp in migratory breeding populations in rivers, and the annual population numbers in lakes and rivers, calculate the sex ratio of naked carp in lakes and rivers. S5. Calculate the repeat reproduction coefficient based on the annual population size and repeat reproduction time difference in lakes and rivers. S6. Based on the repeatability coefficient and the sex ratio of naked carp, establish the relationship between the sex ratio of rivers and lakes; S7. Based on the relationship between the male-to-female ratio in rivers and lakes and the repeat reproduction coefficient, predict the total future population of naked carp in lakes.

[0008] Furthermore, in S1, the population vectors of female and male naked carp in the lake are represented as follows:

[0009] In the formula, For the first Annual lake female fish population vector; For the first Annual population vector of male fish in lakes; For the first Lake Number of female fish of the same age; For the first Lake Number of male fish of the appropriate age; , These are the maximum ages of the female and male fish, respectively, expressed in years (a). This represents the transpose of a vector.

[0010] Furthermore, in S2, the population vectors of female and male naked carp in the migratory breeding population of the river are represented as follows:

[0011] In the formula, For the first Annual river female fish breeding population vector; For the first Annual river male fish breeding population vector; , These represent the minimum and maximum reproductive ages of the female fish, respectively. , These represent the minimum and maximum reproductive ages of male fish, respectively.

[0012] Furthermore, in S3, the annual population size of lakes and rivers is calculated; The lake population size is as follows:

[0013] In the formula, For the first Total number of female fish in lakes in a given year; For the first Total number of male fish in lakes in a given year; For the first Year Lake Total number of fish of all ages; For the first Total annual population of naked carp in lakes; The river breeding population size is:

[0014] In the formula, For the first Total number of female fish breeding populations in rivers in a given year; For the first Total number of male fish breeding populations in rivers each year; For the first The annual breeding population of naked carp in rivers.

[0015] Furthermore, in step S4, the sex ratio of naked carp in lakes and rivers is calculated, and expressed as follows:

[0016] In the formula, For the first Year Lake The sex ratio of fish at a specific age; For the first Annual overall sex ratio of lakes; For the first River of the Year The sex ratio of fish at a specific age; For the first Annual comprehensive female-to-male ratio of rivers.

[0017] Furthermore, in step S5, the repeatability coefficient is calculated, which is expressed as:

[0018] In the formula, The repeatability coefficient for female fish represents the number of times a parent fish enters a river to participate in reproduction during its lifetime. The repeatability coefficient for male fish; This is to allow for repeated reproduction time differences.

[0019] Furthermore, in S6, the relationship between the male-to-female ratio of rivers and the male-to-female ratio of lakes is expressed as follows:

[0020] In the formula, The sex ratio of an i-year-old migratory breeding population in a river in year t is a specific age-specific ratio, that is, the ratio of the number of female fish to the number of male fish in that age group.

[0021] Furthermore, in S7, the predicted total resource quantity of naked carp in the lake in the future is expressed as follows:

[0022] In the formula, For the first Total annual population of naked carp in lakes; This represents the average natural growth rate of naked carp across different age groups.

[0023] The method for predicting fish resources based on changes in the sex ratio provided by this invention has the following beneficial effects: This invention constructs a specific age-specific sex ratio and a comprehensive sex ratio for lakes and rivers, combined with the sex ratio linkage relationship, to accurately reflect the dynamic differences in sex ratios of different age groups. At the same time, it incorporates a repeat reproduction coefficient to quantify the reproductive contribution of parent fish throughout their life cycle, avoiding estimation biases caused by single sex ratio or single reproduction assumptions, and making the calculation of the number of effective breeding individuals more consistent with the actual reproductive characteristics of fish.

[0024] Based on the ecological habits of migratory fish that "inhabit lakes and reproduce in rivers", this invention constructs lake population vectors and river reproduction population vectors to achieve accurate calculation of population size. By combining the sex ratio characteristics and reproduction coefficient of the river reproduction population with the lake population base, the connection logic between population replenishment and existing resource quantity is more complete, and the prediction error caused by data isolation is significantly reduced. Attached Figure Description

[0025] Figure 1 This is a flowchart illustrating a method for predicting fish resources based on changes in the sex ratio, as an example. Detailed Implementation

[0026] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0027] The changes in the sex ratio of naked carp in Qinghai Lake and its impact on the naked carp population have not yet received sufficient attention and relevant research. This is an important scientific issue that urgently needs to be addressed in the future conservation of naked carp in Qinghai Lake, including a series of issues such as population, environment, genetics and molecular mechanisms. Qinghai Lake is an oligotrophic, high-altitude brackish lake with approximately six months of ice cover each year (from mid-October to early April of the following year). The development of the gonads of broodstock naked carp from stage II to stage III and then to stage IV requires a considerable amount of time. Their gonads do not mature and they cannot enter the river to participate in reproduction every year, resulting in intermittent reproduction and differences between males and females. This embodiment defines the repeatability coefficient of male and female broodstock as the average number of times a broodstock participates in reproduction throughout its lifetime. This is an important parameter in the naked carp population model. Given the background of "more females than males" in lakes and "fewer females than males" in rivers, the number of reproductions by male and female broodstock is of particular significance for maintaining the stability and reproduction of the Qinghai Lake naked carp population. The specific values ​​of the sex ratio vary considerably, mainly affected by sampling location, time, and sample size. Recent sample sizes and representativeness have been insufficient. For example, the sex ratio sample size for lakes was only 327 individuals (2002-2003) and 273 individuals (2024). The age structure of naked carp in lakes is mainly 1-10 years old, making the sample size insufficient when distributed across different age groups. Furthermore, lake sampling points do not yet cover the main distribution areas of different naked carp populations. River sampling points are concentrated in the lower reaches of rivers, necessitating the increase of sampling points and sample sizes in the upper and middle reaches. Therefore, this embodiment aims to increase the field sampling efforts in lakes and rivers, achieving a sample size of over 1000 individuals (non-destructive survey) to obtain more accurate and representative sex ratio values ​​for lakes and rivers. Based on this, this embodiment provides a method for predicting fish resources based on changes in the sex ratio, referencing... Figure 1 Specifically, it includes the following: S1. Construct the population vectors of female and male naked carp in the target lake, which are represented as follows:

[0028] In the formula, For the first Annual lake female fish population vector; For the first Annual population vector of male fish in lakes; For the first Lake Number of female fish of the same age; For the first Lake Number of male fish of the appropriate age; , These are the maximum ages of the female and male fish, respectively, expressed in years (a). This represents the transpose of a vector.

[0029] S2. Construct the population vectors of female and male naked carp in the migratory breeding population of the target lake's rivers, represented as follows:

[0030] In the formula, For the first Annual river female fish breeding population vector; For the first Annual river male fish breeding population vector; , These represent the minimum and maximum reproductive ages of the female fish, respectively. , These represent the minimum and maximum reproductive ages of male fish, respectively. S3. Calculate the annual population size of lakes and rivers based on the population vectors of female and male fish in lakes and rivers. The lake population size is as follows:

[0031] In the formula, For the first Total number of female fish in lakes in a given year; For the first Total number of male fish in lakes in a given year; For the first Year Lake Total number of fish of all ages; For the first Total annual population of naked carp in lakes; The river breeding population size is:

[0032] In the formula, For the first Total number of female fish breeding populations in rivers in a given year; For the first Total number of male fish breeding populations in rivers each year; For the first The annual breeding population of naked carp in rivers.

[0033] S4. Based on the population vectors of female and male naked carp in lakes, the population vectors of female and male naked carp in migratory breeding populations in rivers, and the annual population numbers in lakes and rivers, calculate the sex ratio of naked carp in lakes and rivers. This embodiment explicitly defines two concepts of sex ratio in lakes and rivers. One is called the "age-specific sex ratio," which refers to the ratio of female to male fish counted according to age, reflecting the impact of environmental changes in the year of birth on the sex ratio. This concept has been used in population sex studies but is a new concept in fish sex studies. The other is called the "integrated sex ratio," which refers to the traditional sex ratio concept that does not distinguish between age.

[0034] Based on this, the sex ratio of naked carp in lakes and rivers is calculated and expressed as follows:

[0035] In the formula, For the first Year Lake The sex ratio of fish at a specific age; For the first Annual overall sex ratio of lakes; For the first River of the Year The sex ratio of fish at a specific age; For the first Annual comprehensive female-to-male ratio of rivers.

[0036] S5. Based on the annual population size and repeat reproduction time difference in lakes and rivers, calculate the repeat reproduction coefficient, which is expressed as:

[0037] In the formula, The repeatability coefficient for female fish represents the number of times a parent fish enters a river to participate in reproduction during its lifetime. The repeatability coefficient for male fish; This is to allow for repeated reproduction time differences.

[0038] The Qinghai Lake naked carp is a repeat-spawning species with reproductive intervals, spawning synchronously in batches. The majority of breeding populations are 4-5 years old, with individuals over 8 years old being a minority. Separately, the youngest breeding age for males is 3 years, and for females, it is 4 years. After spawning, the gonads of the Qinghai Lake naked carp regress to stage II, and they quickly return to the lake to feed and grow. Therefore, the parent fish need to complete gonad development from stage II to stage IV in Qinghai Lake before returning to rivers to reproduce. Qinghai Lake is an oligotrophic lake, and the low temperature environment slows down the gonadal and growth development of the naked carp. It takes at least a year for gonad development from stage II to the end of stage III. Current research indicates that stage IV gonad development in the lake requires a year from the initial to the final stage. Therefore, it takes approximately 2-3 years for the Qinghai Lake naked carp to develop from stage II gonads to stage IV gonads, which are suitable for migratory reproduction. The male's repeat reproductive coefficient should be 2-3 times, with a maximum of 4 times. Considering that the female's ovary development requires more resources, the female will reproduce 1-2 times in her lifetime, with a maximum of 3 times. Therefore, theoretically, the average range of the repeat reproductive coefficients for both male and female fish is:

[0039]

[0040] S6. Based on the repeatability coefficient and the sex ratio of naked carp, establish the relationship between the sex ratio of rivers and lakes, expressed as follows:

[0041] In the formula, The sex ratio of an i-year-old migratory breeding population in a river in year t is a specific age-specific ratio, that is, the ratio of the number of female fish to the number of male fish in that age group.

[0042] S7. Based on the relationship between the male-to-female ratio in rivers and lakes and the repeat breeding coefficient, predict the total future population of naked carp in lakes:

[0043] In the formula, For the first Total annual population of naked carp in lakes; This represents the average natural growth rate of naked carp across different age groups.

[0044] To verify the accuracy of the predictions in this embodiment, a sample of 1,000 fish was observed in the Qinghai Lake area, rivers (Buha River, Heima River, and Quanji River), and the released population. Sexes were identified by the shape of the anal fin, and the total length was measured. A total of 5,000 fish were collected to obtain typical and representative sex ratio and total length data.

[0045] Lake Area Survey: In conjunction with the annual lake area resource surveys conducted in April and September, a sex ratio survey of naked carp will be carried out. The sampling area should cover the main distribution areas of naked carp in the lake, including the saline water areas of the estuaries of the five main rivers flowing into the lake. Naked carp of different ages (total length) over one year old will be collected using different nets. The sample size is 1000 fish. Using traditional morphological methods and a fish measuring rod, total length will be measured non-destructively (age will be estimated based on the total length-age relationship in the standard growth model of naked carp) and sex will be determined to obtain age and sex ratio.

[0046] River Survey: In conjunction with artificial breeding operations from June to August each year, a sex ratio survey of naked carp is conducted in the middle of each month across the entire basin of the Buha River, Heima River, and Quanji River. Sampling areas cover the upper, middle, and lower reaches of the rivers, collecting upstream migrating individuals. A sample size of 1000 individuals is collected from each river. Using traditional morphological methods and a fish measuring tape, total length is measured non-destructively (to estimate age) and sex is determined to obtain age and sex ratio.

[0047] Stock enhancement and release survey: 1000 individuals are randomly sampled from the annual stock release. Using traditional morphological methods and a fish measuring tape, the total length is measured non-invasively (to estimate age) and sex is determined to obtain age and sex ratio.

[0048] Although specific embodiments of the invention have been described in detail with reference to the accompanying drawings, this should not be construed as limiting the scope of protection of this patent. Various modifications and variations that can be made by a person skilled in the art without inventive effort within the scope described in the claims still fall within the scope of protection of this patent.

Claims

1. A method for predicting fish resources based on changes in the sex ratio, characterized in that, Includes the following steps: S1. Construct the population vectors of female and male naked carp in the target lake; S2. Construct population vectors for female and male naked carp in the migratory breeding population of naked carp in the target lake's rivers; S3. Calculate the annual population size of lakes and rivers based on the population vectors of female and male fish in lakes and rivers. S4. Based on the population vectors of female and male naked carp in lakes, the population vectors of female and male naked carp in migratory breeding populations in rivers, and the annual population numbers in lakes and rivers, calculate the sex ratio of naked carp in lakes and rivers. S5. Calculate the repeat reproduction coefficient based on the annual population size and repeat reproduction time difference in lakes and rivers; S6. Based on the repeatability coefficient and the sex ratio of naked carp, establish the relationship between the sex ratio of rivers and lakes; S7. Based on the relationship between the male-to-female ratio in rivers and lakes and the repeat reproduction coefficient, predict the total future population of naked carp in lakes.

2. The method for predicting fish resources based on changes in the sex ratio according to claim 1, characterized in that, In S1, the population vectors of female and male naked carp in the lake are represented as follows: In the formula, For the first Annual lake female fish population vector; For the first Annual population vector of male fish in lakes; For the first Lake Number of female fish of the same age; For the first Lake Number of male fish of the appropriate age; , These are the maximum ages of the female and male fish, respectively, expressed in years (a). This represents the transpose of a vector.

3. The method for predicting fish resources based on changes in the sex ratio according to claim 2, characterized in that, In S2, the population vectors of female and male naked carp in the migratory breeding population of the river are represented as follows: In the formula, For the first Annual river female fish breeding population vector; For the first Annual river male fish breeding population vector; , These represent the minimum and maximum reproductive ages of the female fish, respectively. , These represent the minimum and maximum reproductive ages of male fish, respectively.

4. The method for predicting fish resources based on changes in the sex ratio according to claim 3, characterized in that, In S3, the annual population size of lakes and rivers is calculated; The lake population size is as follows: In the formula, For the first Total number of female fish in lakes in a given year; For the first Total number of male fish in lakes in a given year; For the first Year Lake Total number of fish of all ages; For the first Total annual population of naked carp in lakes; The river breeding population size is: In the formula, For the first Total number of female fish breeding populations in rivers in a given year; For the first Total number of male fish breeding populations in rivers each year; For the first The annual population size of naked carp breeding in rivers.

5. The method for predicting fish resources based on changes in the sex ratio according to claim 4, characterized in that, In step S4, the sex ratio of naked carp in lakes and rivers is calculated and expressed as follows: In the formula, For the first Year Lake The sex ratio of fish at a specific age; For the first Annual overall sex ratio of lakes; For the first River of the Year The sex ratio of fish at a specific age; For the first Annual comprehensive female-to-male ratio of rivers.

6. The method for predicting fish resources based on changes in the sex ratio according to claim 5, characterized in that, In step S5, the repeatability coefficient is calculated and expressed as follows: In the formula, The repeatability coefficient for female fish represents the number of times a parent fish enters a river to participate in reproduction during its lifetime. The repeatability coefficient for male fish; This is to allow for repeated reproduction time differences.

7. The method for predicting fish resources based on changes in the sex ratio according to claim 6, characterized in that, In S6, the relationship between the male-to-female ratio of rivers and the male-to-female ratio of lakes is expressed as follows: In the formula, The sex ratio of an i-year-old migratory breeding population in a river in year t is a specific age-specific ratio, that is, the ratio of the number of female fish to the number of male fish in that age group.

8. The method for predicting fish resources based on changes in the sex ratio according to claim 7, characterized in that, In S7, the predicted total resource quantity of naked carp in the lake in the future is expressed as follows: In the formula, For the first Total annual population of naked carp in lakes; This represents the average natural growth rate of naked carp across different age groups.

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