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# SC/69A/CMP/01

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### Resource ID

19958

### Access

Open

### Document Number

SC/69A/CMP/01

### Full Title

The Southwestern Atlantic Southern Right Whale, Eubalaena australis: updated population rate of increase

### Author

Enrique A. Crespo, Mariano A. Coscarella And Nicolas Sueyro

### Authors Summary

The paper assesses the rate of increase and a relative abundance estimate for the Peninsula Valdés, Argentina; the main breeding ground of the Southwestern South Atlantic Ocean stock. The results indicate that the calves in PV are still growing at a 2.55% annual rate (95%CI = 0.47% - 4.63%). Nevertheless, the increasing rate is decreasing -0.336% annually since 2007. Also, data indicates that the total number of whales in the area counted by areas surveys has reached a plateu.

### Publisher

IWC

### Publication Year

2023

### Abstract

This paper reports on aerial surveys conducted to estimate the relative abundance and trend in the growth of the southern right whale (Eubalaena australis) population from Península Valdés. The number of whales counted tripled from 1999 to 2022. After the interruption during the COVID pandemic, we resumed the aerial surveys. We modelled the number of whales, the number of calves, the number of Solitary Individuals and the number of individuals in Breeding Groups using as predictive variables the Year, the Julian day and Julian day2 by means of generalized linear models.

The rate of increase es estimated at 0.32 (95% IC= -1.45% – 2.08%), for the total number of whales and from 7.5% in 2007 to 2.55% (95%CI = 0.47% - 4.63%). for the number of calves, respectively for 2022. For both response variables (whole population and calves), no other model presents a ΔAIC less than 2, hence no other model but the selected one was supported by the data. For 2007, the rate of increase was 8.20% and decreased at a rate of -0.604% annually (Linear regression, P < 0.001). For the calves, the rate of increase fluctuated from 7.45% to 2.55% during the same period. The regression model shows a milder decrease in the trend for the calves’ increasing rate (-0.336% annually; Linear regression, P = 0.009). We conclude that whales are still increasing their abundance, while the rate of increase starting to fluctuate near zero for the total number of whales and it continues to be positive for the calves. Additionally, the solitary individuals and the mating groups are decreasing in the area, Differences in the rates of increase of the group types and changes in habitat use are a consequence of a density dependence process.

This paper reports on aerial surveys conducted to estimate the relative abundance and trend in the growth of the southern right whale (Eubalaena australis) population from Península Valdés. The number of whales counted tripled from 1999 to 2022. After the interruption during the COVID pandemic, we resumed the aerial surveys. We modelled the number of whales, the number of calves, the number of Solitary Individuals and the number of individuals in Breeding Groups using as predictive variables the Year, the Julian day and Julian day2 by means of generalized linear models.

The rate of increase es estimated at 0.32 (95% IC= -1.45% – 2.08%), for the total number of whales and from 7.5% in 2007 to 2.55% (95%CI = 0.47% - 4.63%). for the number of calves, respectively for 2022. For both response variables (whole population and calves), no other model presents a ΔAIC less than 2, hence no other model but the selected one was supported by the data. For 2007, the rate of increase was 8.20% and decreased at a rate of -0.604% annually (Linear regression, P < 0.001). For the calves, the rate of increase fluctuated from 7.45% to 2.55% during the same period. The regression model shows a milder decrease in the trend for the calves’ increasing rate (-0.336% annually; Linear regression, P = 0.009). We conclude that whales are still increasing their abundance, while the rate of increase starting to fluctuate near zero for the total number of whales and it continues to be positive for the calves. Additionally, the solitary individuals and the mating groups are decreasing in the area, Differences in the rates of increase of the group types and changes in habitat use are a consequence of a density dependence process.