An evaluation method for the priority protection of fishes based on multiple ecological dimensions

Abstract It’s essential to identify the priority conservation species in the habitat restoration and biodiversity conservation. Generally, people select the valuable fishes or the commercial fishes as target species in basins, according to experts’ experience rather than the scientific evaluation. With the influence of urban development, construction of water conservancy facilities and human activities, the river habitat of the Shaying River (Xuchang section) is poor. Fish conservation studies play an important part in the habitat restoration of this river section. Thus, we studied the evaluation method for the priority protection of fishes based on multiple ecological dimensions. The method including six multidimensional indicators, namely, habitat suitability, ecological stability, species endangerment criteria, intensity of human interference, genetic value, and species value. Then, we determined the indicator weights by the analytic hierarchy process (AHP), and assessed the protection priority of fishes based on various assessment criteria and comprehensive qualitative or quantitative analyses. The result shows that Ctenopharyngodon idellus, Opsariichthys bidens, and Culter alburnus Basilewsky have priority for protection, coinciding with the status in the basin. Overall, this study complements the existing indicator species selection methods, and is more scientific and comprehensive, providing an effective method for priority protection species and river habitat restoration projects.


Introduction
Global climate change and frequent human activities have led to alteration and even extensive loss of river habitats.It brings a series of negative effects on the habitat and reproduction of aquatic organisms, biological resources, and diversity (Collen et al. 2014; CONTACT Yanpeng Wang wangyanpeng08@163.comMunicipal engineering design Institute, Zhengzhou University Multi-functional Design and Research Academy CO LTD, Zhengzhou, China Supplemental data for this article can be accessed online at https://doi.org/10.1080/02705060.2022.2144956.

Watershed background data collection
In the early stage of the study, data collecting is necessary, includingenvironmental history data, habitat status data, and biological recording data.In this study, we chose Shaying River (Xuchang section) as the study sample, which is 149 km long with a basin area of 2362 km 2 .In October 2015 and August 2016, fish surveys revealed the habitat conditions in the basin were poor and not conducive to the healthy growth of fish (Min et al. 2016).
Additionally, a rapid bioassessment protocol (RBP) habitat survey and evaluation of the Shaying River showed that the upper and middle reaches of the basin were poorly developed and provided poor living and reproduction conditions for aquatic organisms (Zhang 2018).The fish resources in this river section shows high diversity index, diversified characteristics in feeding, breeding and habitat habits (Chen, G et al. 2017).

Selection of evaluation indexes and determination of evaluation criteria
Drawing on the studies of existing assessment at home and abroad, quantitative indicators should be selected as far as possibly to avoid the errors arising from subjective judgments.Many scholars focused on the species distribution, genetic characteristics, habitat requirements, rare and endangered criteria, vulnerability, and economic value to study the protection of fish (Hermoso et al. 2013;Hermoso et al. 2016;Olden and Naiman 2010;Patrick et al. 2010;Strecker et al. 2011).To make it more comprehensive and accurate in the assessment about the priorities of fish conservation, we formulate an evaluation system with six multidimensional indicators including habitat suitability, ecological stability (Evans et al. 2015;Nel et al. 2009), species endangerment criteria (Takimoto and Post 2013)., intensity of human interference (Teichert et al. 2016), hereditary value (Hermoso et al. 2013;Hermoso et al. 2015;Leitão et al. 2016) and species value.We use the above six characteristics as first-level indicators, and select two second-level indicators for each first-level indicator.These indicators profiles and selection criteria are as follows.

Habitat suitability
Although the tolerance level of chemical and physical habitats varies among fish, it is undeniable that clean water and good habitat will promote the growth of fish.
a. Physical habitat: We used the method River Habitat Survey (RHS), which includes physical factors such as water depth, flow velocity, riverbed substrate, and riverbed geomorphological characteristics, covering a total of 16 evaluation indicators of habitat parameters.According to the survey results, there are four standards: good, medium, bad and worse, which have increasing priority protection requirements.b.Chemical habitat: Water pollution will have an impact on the structure and density of fish populations.This indicatoris determined by the water quality, according to the Water grades, which mainly refers to COD, TN, TP, NH3-N, etc.And the assessment criteria are divided into four standards: Grade I $ III water, Grade IV water, Grade V water, worse than Grade V water.They have increasing priority protection requirements.c.Ecological stability Traditional biodiversity conservation considers interspecific interactions and ecological niche relationships as determinants of ecological structure stability.Recently ecologists have begun to focus on interactions at the spatial scale.Fish resources in Xuchang were divided into upper, lower, bottom layer about the vertical distribution of water layers.The density of fish distribution was different in different water layer structures, and the weaker the fish distribution was the more vulnerable to external environmental influences (Chen, G et al. 2017).The structure of the aquatic ecosystem is also closely related to the complexity of the food web.The transfer efficiency of natural systems is usually only about 10% (Oikonomou et al. 2018;Takimoto and Post 2013).Species with high nutrient levels are prone to extinction.Meanwhile, the loss of top consumers may have serious consequences for the stability of the food web.Besides, individual ecological fishes of single feeding habitats are always weaker.Therefore, top predators are more likely to be extinct than low-trophic species, while high-trophic species (especially individual ecological fishes) have higher protection values.a. Water layer structure: This indicator requires a dynamic balance of fish species in each vertical space.In the survey samples, the distribution of fish in different water layers varied.There are four layers we divided: the surface layer, the upper layer, the lower middle layer and the bottom layer.The higher the layers, the lower the fish density and the higher the conservation priority.b.Food web structure: This indicator takes into account the nutritional level and feeding habitats of fish.The four types of feeding habitats, namely complete carnivore, herbivore, mainly carnivorous, omnivore, have the decreasing priority protection needs c.Species endangerment criteria Usually, the protection of rare and endangered species is the basic work in ecosystem protection.When there is endangered species in the basin, it should be selected as a priority species for protection directly.The rarity and endangerment of fish reflected in this indicator is not a property of fish, but a reflection of the difference in survival status of fish relative to other fish in the basin.It is mainly reflected by the frequency of occurrence and relative quantity.a. Occurrence frequency: It refers to the ratio of sampling sites where one species was present to the total number of sampling sites.The lower the frequency of occurrence, the narrower the distribution range, the higher the rarity.This indicator is divided into four levels of criteria based on the survey sample: 0 to 5, 5 to 10, 10 to 20, 20 to 100 (%), which has decreasing priority protection needs.b.Relative quantity: This indicator is the ratio of the number of one species occurrence to the total number of fish occurrences.This indicator also has four standards:0 to 1, 1 to 5, 5 to 10, 10 to 100 (%), and these standards have decreasing priority protection needs.c.Intensity of human interference This index is a qualitative index.It reflects the degree of human interference by analyzing external factors.It is mainly reflected by the degree of disturbance in the spawning environment and habitat environment.
1. Degree of disturbance in the spawning environment: The dams and gates seriously interferes with the normal seasonal hydrological variation of rivers.Due to the changes in water depth and flow velocity, the fish that require the spawning environment are seriously affected.Practitioners judge the hydrological changes in the basin based on historical hydrological data, and the spawning needs of different fish is also concerned in evaluation.2. Degree of habitat disturbance: The daily habitat activities of fish in the watershed are closely related to human activities such as overfishing.This indicator is based on the weight of fish caught in each sampling site.Then we can calculate the fish resource density (g/net) to judge the degree of interference of overfishing.The lower the resource density, the more disturbed it is.These two secondary indicators can be divided into four standards: serious , moderate interference, mild interference , near nature.

Genetic value
Genetic value is included in conservation plan to ensure and maintain the evolutionary process of biodiversity.It refers to the potential genetic loss of a fish species to its ecosystem after extinction.It is a quantitative evaluation of the potential genetic value of the species, according to the study of Song et al. (2018).
1. Species type: With the loss of endangered species, the diversity of the community decreases.This indicator analyzes the distribution of the fish genus in the basin, and is divided into four types: sole genus, 2 species' genus, 3 species' genus, genus with more than 3 species.2. Endemism: This is determined by whether the fish are currently endemic to the watershed Endemic species usually face a higher risk of extinction.This indicator looks at whether the surveyed fish are endemic to this basin, distributed in two waters, distributed in three to four waters, or widely distributed types.

Species value
This indicator judges the value of species from the human perspective, which mainly includes two aspects: economic value and ecological value.
1. Economic value: In terms of the contribution to the economic benefits of fishery resources, priority was given to the fish with high economic value.There are four standards: main breeding objects, important economic species, species of some value, no economic value species.2. Ecological value: This indicator was used to protect ecologically disadvantaged fish.
While the relative importance index (IRI) of Pinkas was usually used to determine the dominance of species.The IRI contains important information on the number of individuals, biomass, and frequency of occurrence of a species.It is calculated as equation 1.
where N refers to the percentage of individuals of a certain species relative to the total number of individuals; W refers to the weight percentage of a certain species relative to the total weight, and F refers to the percentage of the stations at which a certain species is identified relative to the total number of surveyed stations.This study classifies species with an IRI ! 10 as dominant species, species with 5 IRI < 10 as common species, species with 1 IRI < 5 as general species, and species with IRI < 1 as subordinate species.
All the above indicators are summarized in Table 1.

Determination of index weights and consistency test
In this study, the weight of the indicators was determined by the analytic hierarchy process (AHP).We judged the importance of each element based on existing research, practice, and expert experience.Then we built the judgment matrix, and calculated the weights of each indicator by MATLAB.Finally, in order to avoid the interference of subjective consciousness on the properties of complex things themselves, we checked the consistency test.When CR < 0.10, the judgment matrix has satisfactory consistency.The weights of the indexes are shown in Table 2.

Comprehensive evaluation calculation method
According to the above study and survey of Shaying River (Xuchang section), we calculate the priority evaluation value for each fish species (R).The calculation formula is as Equation 2.
where The number of priority protected species should be greater than the sum of the mean and standard deviation of the number of studied species; that is R > R mean þ R SD :

Habitat suitability survey
In August 2018, we selected 20 sampling sitesto investigate the fish resources of their major tributaries in Shaying River (Xuchang section).It mainly involved the Shahe River mainstream, Shiliang River, Xufu Canal, Yinma River, Qiling River, Furong Lake, East Lake, Qiuhu Wetland, and other rivers.The locations of the sampling sites are shown in Figure 1.In Chen Guoqiang's survey, 33 species of fish were counted in Xuchang, belonging to 28 genera in 10 families of 5 orders, with the most Cypriniformes, followed by Perciformes, and fewer other species (Chen, G et al. 2017).We collected 20 species of fish, belonging to 5 orders, 10 families, and 19 genera, with the most Cypriniformes (12 species), followed by Perciformes (4 species), and fewer other species.This is consistent with the distribution of fish resources in Xuchang.
In this study, the status of watershed habitat was investigated three times in October 2015, August 2016, and December 2016.The physical habitat status was shown in Figure 2. The poor physical habitat in the upper and middle reaches of the river is mainly due to the high intensity of artificial disturbance and the lack of ecological base flow.The physical habitats of Shiliang River, Yingru Canal, and Xiaohong River are the best, while the physical habitats of other reaches are general.The chemical habitat status is shown in Figure 3.The overall distribution of water quality in the basin is poor.Compared with the fish survey data, most of the dozens of fish species, such as smelt, rounded tail, and betta, were located in the river reach with poor physical habitat or poor habitat.While most of the nine species of fish were located in the river reach with poor chemical habitat or poor habitat.

Ecological stability
The ecological structure of fish in the target watershed is shown in Table 3.The surveyed fish were distributed in all water layers, the percentages of surface layer, the upper layer, lower layer, and bottom are 5%, 25%, 25%, and 45%.According to the type of feeding, the proportions of different fish diets were 5%, 5%, 40%, and 50% for a complete carnivore, herbivore, mainly carnivorous, and omnivorous in that order.Obviously, carnivorous and omnivorous fishes were the main species identified in this survey.

Species endangerment criteria
The fish resource survey results (Figure 4) revealed that Acheilognathus macropterus, Acheilognathus tonkinensis, and Pseudorasbora parva were relatively abundant.Among these species, A. tonkinensis accounted for more than half of all individuals.There were many occurrences of Abbottina rivularis, A. macropterus, and P. parva, among which P. parva was the most frequent.And the relative numbers and frequencies of nearly half of the fish, such as Opsariichthys bidens, Pelteobagrus fulvidraco, and Rhodeus ocellatus were relatively low.From correspondences with anglers and fisheries management departments, we learned that the diversity of fish species throughout the basin has been declining.To a certain extent, this trend suggests that the distribution and quantity of fish in this basin are declining.Scholars analyze that it may be related to inadequate resource protection, habitat destruction, overexploitation, and overutilization.

Intensity of human interference
The habitat and spawning characteristics of fish in the Shaying River (Xuchang section) are shown in Table 4.According to habitat characteristics, there were three categories of spawning, namely, hydrostatic settlement, ravine settlement, and semi-migration, with the proportion of 60%, 25%, and 15% respectively.Most of the fishes laid demersal eggs and viscid eggs, while a few fishes laid semi-pelagic eggs.Because of the frequent human activities in Shaying River (Xuchang section), the ecological environment of the rivers is severely damaged, and the submerged plant resources are scarce.Therefore, the rivers in this basin are not conducive to the hatching of semi-pelagic eggs and viscid eggs and are more conducive to the hatch of demersal eggs.In addition, since the river flows through Xuchang city, there is substantial human influence through activities such as artificial fishing.It causes the average age of the fish in the watershed to decrease and thus is not conducive to the health or development of the fish.

Genetic value and species value of fishes
According to the analysis of the genetic value of fishes (Table 5) in the Shaying River, the only monotypic species was C. idellus, and the other fish species were common.There were no endemic species, and all species were widely distributed.On the basis of species value, the dominant species were mainly P. parva, A. macropterus, and A. tonkinensis.
The less valuable species were C. idellus, O. bidens, R. ocellatus, P. fulvidraco, and Macropodus chinensis.There were many economic fishes in the watershed, and many of them were ornamental fishes.

Conservation species screening results
The priority protection values of fishes in the Shaying River (Xuchang section) were comprehensively evaluated, the results are shown in Table 6.There were three species of fish that are priority protected fish species: Ctenopharyngodon idellus, Opsariichthys bidens, and Culter alburnus Basilewsky, which accounted for 15% of the total number of fishes in the Shaying River (Xuchang section).

Discussion
In previous habitat restoration and fish protection practices, people mainly selected endangered fish or major commercial fish as conservation targets according to the experts' experience.It ignores the multidimensional characteristics of fish and has greater subjectivity and geographical limitations to some extent.In the study of the optimization of selection methods, some scholars consider a single indicator.For example, Sarkar et al. analyzed fish diversity as well as the distribution range of the fish in the Ganges River basin to obtain the diversity index and evenness index of each fish species.Then they screened the conservation species, which is in line with the local geographical situation (Sarkar et al. 2012); Beger et al. studied the fish conservation priorities based on the hydrological conditions, fish breeding, and foraging characteristics to study the fish conservation priorities.They took the influence of different waterenvironments on fish diversity into account.At the same time, they studied the interconnection between breeding and foraging factors and connected water, which is a breakthrough from other studies.(Beger et al. 2010); Esselman et al. used Marx, GIS to delineate the network of protected areas to study the influence of macroscopic distribution range on fish conservation priorities and protected area planning.These scholoars' studie reflects the importance of fish distribution range macroscopically and conventionally on fish conservation and watershed conservation planning (Esselman and Allan 2011); Song Yiqing et al. studied the method of evaluating fish conservation priority order from genetic value, species value, and endangerment criteria (Song et al. 2018).But to some extent, it ignores the relationship with the ecosystem, the ecological structure.The above assessment factors have been of great concern to researchers (Lima et al. 2017).We can find that these studies provide good references and experience for people's habitat restoration and biodiversity conservation work.However, the study of a single factor often has limitations and geographical restrictions.This study combined mature habitat assessment models and practical experience in habitat restoration and fish protection at home and abroad.We selected six first-level indicators that can reflect the ecological multidimensionality, namely, habitat suitability, ecological stability, species endangerment criteria, intensity of human interference, genetic value, and species value.Meanwhile, we also selected 12 secondary indicators to establish the evaluation system.Then the evaluation criteria and weights of each indicator were also determined.To guarantee the rationality and consistency of the system, the weights of each indicator were obtained by AHP.The assessment criteria are based on existing studies and survey samples.The fish conservation priority assessment refers to the relative priority among fish in the watershed.Actually, the distribution of habitats and fish resources vary from basin to basin, the assessment criteria for some secondary indicators in this study are hardly universal.Thus, appropriate criteria can be developed based on the historical information of the watershed and the sample data to ensure the successful assessment in practical application.
In this study, the ecological structural characteristics and environmental status of fish in the Shaingying River (Xuchang section) were studied as an example.We calculated comprehensive evaluation values of the 20 species of fish investigated for priority protection, and selected C. idellus, O. bidens, and C. alburnus as priority species for protection.It is shown that fish conservation strategies must consider the life-history traits and habitat requirements of migratory species.Thus, migratory species are often the focus of fish conservation (Sarkar et al. 2012).Firstly, among them, C. idellus is an herbivore with high ecological value and is a semi-migratory fish.In recent years, numerous dams in the Sand Camp River basin have created insurmountable barriers to fish migration, which leads to habitat degradation.Also, due to overfishing, blind inbreeding, and habitat destruction, C. idellus germplasm resources have begun to be severely degraded facing a high risk of extinction.Thus, the selection of the C. idellus as one of the priority protection species is reasonable.Secondly, the O. bidens is a sedentary stream fish that lays sticky eggs.It is sensitive to the environment.And it occupies an important position in China's freshwater capture fisheries.In recent years, the pollution of the water environment and artificial overfishing has led to the decrease of natural resources of O. bidens.Given that, the O. bidens is a vulnerable species, it deserves to be selected as a priority protection species.At the last, the C. alburnus has high economic value and reproductive migratory habits, whose spawning activities require high hydrological conditions.It is a complete carnivore fish, which plays a protective role in controlling the overpopulation of miscellaneous fish in the basin.So, it plays an important role in maintaining the integrity of the basin food web and ecological balance.The investigation found that C. alburnus is mainly distributed in wide still waters such as the Qingying river and Baling river, where are more suitable to prey and have more bait resources.However, there are many dams in these rivers and cities nearby.Poor habitats and serious artificial disturbances are the main threats to C. alburnus.It is reasonable to select C. alburnus as one of the priority protection species.According to Zhang Wensheng's study and the fish resource survey of Xuchang City (Zhang 2018, Chen, G et al. 2017), the total number and the biomass of C. alburnus in Qingyi River (Xuchang section) are low, and the dominance of C. idellus and O. bidens in the basin are both low.Combining with the research content of this study, it can be seen that the evaluation results in this study are consistent with the actual situation.The evaluation method is accurate and objective, which can make up for the deficiencies of the current species conservation order research in terms of subjectivity and unsound system.It pays more attention to the needs of river ecosystem structure and function, the method provides a scientific basis for the restoration of fish diversity in the watershed.

Figure 1 .
Figure 1.Fish resources sampling sites in Xuchang section of Shaying River Basin.

Figure 2 .
Figure 2. The map of physical habitat assessed.

Figure 3 .
Figure 3.The map of chemical habitat (water quality).

Figure 4 .
Figure 4.The relative numbers and frequencies of fish.

Table 1 .
The evaluation principles for the priority protection level of fishes.

Table 2 .
The setting of indicators' weights.

Table 3 .
Ecological characteristics of fish.

Table 4 .
Habitat and spawning environmental characteristics of fishes.

Table 5 .
Genetic value and species value of fishes.