The species Eubaleana australis has suffered a tremendous loss in population due to fishing gears, vessels traffic, illegal whaling and noise increase in the ocean. The purpose of this study was to identify the changes between the old population of 1937 which was 3369 (Tormosov et al. 1998) to the present day. Previous work has failed to address the changes that this population has experienced. This study was done by analyzing its fertility, survivorship rate, lifespan, sex ratio, and population size based on each age category. This study determined the present-day population was 7000. Also, it showed that a small calf mortality ratio increased which is why this animal is still endangered. This study explained that this population been increasing slowly and steady since the illegal whaling stopped. Also, the threats that this population is encountering have been minimized and this is what lead to the increase. This research can be used for future analysis of nearby populations, to assess the recovery of depleted old populations, and to evaluate new threats and their effects (Fretwell 2014). Overall, the E. australis' population is steadily increasing but it is going to be a long way to recovery.
Introduction
Sea life in this planet has been through a lot of change and most of the time this entails to populations decreasing and increasing throughout time. Sea life is tremendously rich, ranging from very small animals such as shrimps to gigantic one such as whales. These animals have their own unique habitat that if it is disturbed populations might be threatened. This is the case of Eubaleana australis, commonly known as right whales. These types of whales were given their name because they are easily killed and catch. The IUCN redlist classified this species in the order Cetartiodactyla as least concern, but they face modern levels of anthropogenic threats, including habitat degradation and disturbance, principally from coastal development; vessel traffic; and net, fishing gear, or float/buoy entanglement (Allen and Bejder, 2003). The purpose of this study was to determine whether there was a change in the size of the southern right whale population in the southern hemisphere from 1937 to present day.
Southern right whales have a circumpolar distribution; various recognized populations spend part of the year in inshore waters off the coasts of South America, South Africa and Australia, the range of others includes a variety of offshore island areas (Best 1993). In their breeding area off South Africa, southern right whales show a preference for coastal areas, and yet favor certain bays or stretches of coastline over others (Best 2000).
Their reproduction cycle is very slow, females generally have a new calf every three year, therefore producing calves at 3-5-year intervals, usually three years but with a lengthening of the cycle to five years when feeding conditions are poor (Leaper et al. 2006). Because of this, southern right whale population is not stably increasing due to foreign threats. Also, female southern right whales seek sheltered, nearshore waters during the early life-stages of their calves and are more selective of these habitats than non-calving whales; therefore the female will give birth to a single calf after a 12-13 month gestation period (Raymend et al 2014).
This species was extensively exploited in the 18th and 19th century that at one point in history they almost became endangered. Based on Tormosov (1998), Soviet Union made illegal catches between 1951 and 1971 that resulted in a total 3268 captured and killed right whales. This reduced the recovery of this species drastically. Their population is changing because it is adapting to new surroundings, and the most useful signs of the recovery of right whales in recent years is that they are steadily extending their distribution northwards and occupying locations where they have not been seen for a century or more (Richards 2009). He then suggests that this new distribution will take a long time as when before all the commercial whaling began. The population of the 19th century in the southern hemisphere was 10-15 female whales and 20-25 males. This population was being exploited and it almost became endangered (Tormosov et al. 1998). Later on, an agreement was signed in 1935 for the conservation of southern right whales. Since the illegal whaling traffic is ended, whales can reproduce safely. Since that year, there have been a numerous of events trying to prevent the illegal whaling is southern waters.
This species is facing threats as this society evolves, such as ships and vessel traffic. For example, two E. australis were struck by a west-bound passenger ferry just north of Goat Island in Moreton Bay. Two whales sustained massive propeller injuries, and one of these died as a result, the dead E. australis was a 7.1-m female (Lanyon and Janetzki 2016). Of all the "great" whales, right whales are arguably most prone to ship strike due to their surface resting and feeding behaviors, slow swim speed, limited hearing range and consequent lack of response to vessel approach (Terhune and Verboom 1999). These injuries from vessels will likely increase as human migration approaches, because the E. australis will move through coast risking being injured. Previous studies have shown that ship, vessels and fishing gear is a major threat to the southern right whale population. These studies affirm that there is a strong correlation between the decrease of this population and the accidents caused because of these ships (Lanyon and Janetzki 2016).
Another threat that this species is facing is the noise increase in the ocean. E. australis communicate with low-frequency acoustic signal that can be detected for hundreds of kilometers. These whales rely primarily upon acoustic signaling for communication, locating prey and navigation. Because of the high traffic in ships, low-frequency noise has been reported (20-200 Hz) that overlaps acoustic signals used by baleen whales, and increased levels of underwater noise. Reported responses of whales to increased noise include: habitat displacement, behavioral changes and alterations in the intensity, frequency and intervals of calls (Rolland et al. 2012). They discovered this by performing an experiment in Canada after the event of 9/11 and recording levels of hormones. This experiment showed a 6 dB decrease in underwater noise with a significant reduction below 150 Hz. This noise reduction was associated with decreased baseline levels of stress-related faecal hormone metabolites in right whales (Rolland et al 2012).
Another threat that the E. australis is experiencing is the increase in climate change. This is affecting their reproduction and food, which will bring not only the potential for competition with bowheads, but also more predation by killer whales, exposure to novel pathogens, and impacts of invasive species on prey (Moore and Gulland 2014). In years of late ice retreat, the whales are unable to compensate for lost feeding time and suffer reduced calf production and increased calf mortality (Perryman et al. 2002). Reduced sea ice also may allow bowhead whale populations to mix more frequently across the Arctic than they have since the Little Ice Age from the 15th to the 19th century (Heide-Jørgensen et al. 2011)
It was hypothesized that the present-day population size of E. australis in the southern hemisphere would increase compared to the population size in 1937. In other words, the population will increase in a slow steady way because of all the threats that this species encounters such as climate change, vessel traffic, fishing gear entanglement. Also, southern right whales have a tendency to live close off shores, that is why they are easy to approach and therefore kill. Because an agreement was signed in 1935, illegal whaling is not a problem anymore which then leads to a population increase.
Methods
The population of 1937 was obtained from a previous study by Tormosov (1998). He explained that because of the illegal whaling of Soviet ships, the E. australis population was about to became endangered. Given that the southern right whales have a life span of 50-100 years, the data selected for this current study was 10-15 female whales and 20-25 males. Sexual maturity for females is reached between 9 – 11 years which this means that these whales can reproduce, but they can only have one calf per reproduction cycle (Tormosov et al. 1998) Population growth occurred during the first half of the 20th century, but was set back between 1951/1952 and 1970/1971 when Soviet whaling expeditions killed over 3,300 southern right whales illegally (Tormosov 1998). Four populations of Southern Right Whales have been the focus of long-term research efforts (western Australia, eastern South America, and the eastern and western coasts of southern Africa), and all have exhibited apparent annual rates of increase ranging from about 6-14% over various periods of study (Payne et al., 1990). The new population data were located in the paper by Tormosov. The new population was calculated by using excel to do life table calculations and project population sizes.