Various aspects, such as the difficulty in exploring marine habitats and high costs of study are the primary reasons behind the extremely few statistical studies that explore the effects of the population size of marine mammals. As a result, new studies have shown that the lack of ecological data for various endangered species has posed as the most difficult challenge faced any new studies (Reeves & Leatherwood 1994).
Data collected and used in this study is based on the results of previous studies which obtained their data from various Google Scholar sources. The data was then analyzed by the use of VORTEX 10 simulation, a specific method for measuring the risk assessments that occurred to specific population over a span of several years.
(Table 1) Gives the details of reproduction alongside the age structures as presented by Honh et al. (1996). Concerning estimates of age, specific reproduction was used in the VORTEX10. Forage simulation, (Maximum Age of Reproduction) on the other hand, this study made the use of less than the maximum age of Vaquitas to allow the modeling of species that can have post-reproductive lifespans. Additionally, the average age of first male and female offspring is estimated to be 5 years old while at birth, the average sex ratio of newborn offsprings is at 01:01. Therefore, the results of these values indicate that there is an equal population of both the male and females since they both are approximated to be at 50 percent each.
Besides, according to Honh et al 1996, the optimal number of broods per year is 0 while the maximum number of progeny ever recorded was one born (IJsseldijk et al (2014). Due to lack of substantial evidence in ovulation in prior years in the case of pregnant and lactating females, the possibility of giving birth every year is very rare. Consequently, a significant population of female vaquitas does not give birth every year (Honh et al., 1996).As a result, in this particular study, the VORTEX10 simulation was run for adult females in a period of 2 years since the model used suggested that if the average length of time between successive births for adult female was 2 years, then 50% of all adult females were expected to breed in every two years.
The Input values for mortality rates as shown in (Table 1.3) were obtained from different ages of both the male and the female vaquitas (Barlow and Boveng, 1991). However, D'agrosa et al (2000) revealed that the mortality rate is one of the most primary reasons which have led to the extinction of the vaquitas. With their estimated population size, 39 individuals; which is the initial population size were harvested every year. Therefore, the high rise in mortality rates since the initial population size of vaquitas decreased at 60 individuals due to reasons such as; diseases, harvest bycatch, among many others (Barlow and Boveng, 1991). Nevertheless, (PVA 10) was used to estimate the population size of the vaquitas under different scenario so as to simulate the population size over a period of 100 years; and also to model the annual distributions change in probabilities of reproduction and mortality.
(Figure 3) Shows that there is a lack of data that relates to marine mammals on the percentage of males contributing to the breeding pool. Also, Manlik et al. (2016) suggested that the standard model in the estimated of the number of males contribution to the pool of reproduction was (56.5%). (Data summarized in Figure 1 and 3 in the appendices section).
The extremities of environmental catastrophes have significantly affected the reproduction and the survival rates. In this study, two catastrophic events were modeled: The first one comprised of harmful algal bloom catastrophes that result from the rise in the Shannon Dolphin population (Englund et al., 2007). The second one consisting of diseases which can be catastrophic due to the fact that they may affect small populations (Marmontel et al., 1997). (Figure: 5)
The results section plays a crucial role in understanding the exact forces that contribute to the endangerment of the Vaquita species. As a result, this section targets the evaluation of the data gathered in terms of the diverse forces that lead to the reduction of the Vaquita species in the marine environment and consequently lead to the identification of the ideal measures that can be tapped on so as to facilitate in reducing the extinction of the species in their habitats.
Figure: 1.1: The scenario of 100 years simulations of Vaquita populations without environmental Variations and catastrophes
First year Extinction year R
Number of year 1 45 Baseline 49.09 52.64 -0.136
Figure 1:2 shows that the population of Vaquitas will decrease in a period of 100 years simulations and in the absence of harvest practices and severe catastrophes. The number of populations will therefore become extinct in less than 50 years with the significant correlation at R= -0.13
Figure 1.1: Results of 100 years simulations of Vaquita populations under two levels of catastrophes. (n=number of year)
Scenario initial population First year count Extinction year R SD(r)
Disease 60 N=1 N=45 -0.136 0.2911
55.05 0.01 N=1 N=39 Harmful Algal Bloom 60 52.79 0.02 -0.153 0.2882
Table 2.1 shows that under disease scenarios, the initial population decreased gradually from 55.05% to 0.01% at -0.136. Therefore, Vaquitas are approximated to become extinct in the coming 45 years. On the other hand, due to the harmful Algal Bloom the population of Vaquitas is expected to decrease from 52% to 0.02% in 39 years at (r=-0.153)
Figure 2: Results of 100 years simulations of Vaquita populations under two common scenarios of catastrophes with initial population.
Figure: 2 shows that the expected population size of vaquitas in common scenarios such as disease and harvest. According to the graph, the Vaquita population is not sustainable under these conditions. Thus, their extinction is approximated to occur in a period less than 5 years.
In less than 100 years simulations, the population size of vaquitas is expected to have a significant decline due to the effects of various scenarios such as harvests and unfavorable environmental conditions. As this study indicates, the Vaquitas serve as some of the species whose existence is most threatened by economic, environmental, and biological challenges. The economic challenges comprise of the demand for Totoaba by fishermen whose main aim is to meet their expenses after selling the Totoaba. An example of the most common environmental challenges is; the contamination of fresh water in the Gulf region while biological challenges include the form of inbreeding that reduces genetic diversity among the fish.
Since most Vaquitas are captured to lure Totoaba, the by-catch gillnets should be banned in their habitats which, in most cases, are the northern parts of the Californian Gulf. The fishermen affected by such a plan should be provided with alternatives and trained to venture into other economic activities or financial supports that would reduce the supply for Totoaba. The governments involved, such as the United States of America and China should combine efforts and ban the Totoaba trade and as a result. Entirely face out the illegal fishing of Totoaba. Moreover, the judicial punishment should be offered to those engage in illegal fishing. The designs of the fishing nets should be restructured in a manner that would ensure that they capture the required fish rather than the Vaquitas. However, this is not the final solution to protect Vaquita. The Vortex 10 simulation indicated that, regardless of prohibiting by catch gillnets and illegal fishing, the number of Vaquita will extinct in less than 50 years with the mean value at -0.1362 with negative correlation at R= -0.136 (data summarized in Figure 1 and 1.1 in the appendix section ).
Also, dumping of chemicals into the rivers that flow into the Gulf region should be halted. This is because these chemicals pose an environmental hazard to the fish. For example, the scenario of 100 years simulations of Vaquita populations under an environmental catastrophe (Harmful Algal Bloom) shows that the Vaquita population will become extinct in 39 years (R= -0.153)
These might be linked to human activities such as the use of lawns in farmlands and the build-up of the rate of 'overfeeding the algae that exist in the environment. Therefore, the rate of pollution should be reduced and consequently preserve the quality of water in the Gulf area. Penalties should be accorded to any individual or organization that dumps waste into these rivers.
Simulation results indicate that if the percentage of adult female breeding increases from 50% t0 75%, with an increase in the overall population size from 60 to 80 individuals with lower mortality, the probability would be relatively high at the growth to (r = 0.001) (Figure. 8 Appendix). Because of this simulation, the habitats of the Vaquitas should be identified, including the northern Gulf region of California. The region should be distinguished in the sense that, it facilitates in recollecting them in one area and increase the rate of sexual contact. This would play the role of enhancing the rate of breeding and reducing inbreeding. It would also improve the genetic diversity of the animals and enhance their fitness. Such measures should be undertaken by the respective governments to protect the animals from becoming extinct. Therefore, curbing the biological challenges facing Vaquitas can be of great significance for their survival.
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