Dissecting the Evidence Regarding the 1999 Long Island Sound American Lobster Mortality Event​

​In the early 1990’s the American Lobster (Homarus Americanus) population living in the brackish waters of Long Island sound was flourishing. Commercial fishing of lobsters was an important industry for those who lived along the shores of Long Island Sound, it was at its finest. A trawl survey declared the lobster abundance due to a substantial increase in recruit and pre-recruit sized lobsters, also known as the lobsters ripe for reproduction (Benway et al. 2005). Lobstermen in the New York and Connecticut area were reaching unprecedented number in their commercial landings around 1996 and 1997 when they reeled in approximately 11 million pounds of lobster totaling a worth of about $42 million. During this time, about 50-60% of this harvest occurred in the western portion of Long Island Sound (west of Norwalk, CT) (Benway et al. 2005). Beginning in 1998 and intensifying in the fall of 1999, the homarus americanus population experienced a drastic mortality event that had a large impact on the once productive industry of commercial lobster fishing in the western sound. Some lobstermen in this section of the sound experienced a decline of as much as 99% of the landings they had the previous year. In eastern Long Island Sound, lobstermen were experiencing landing reductions ranging from 64%-91%, putting the entire lobster industry of Long Island Sound at jeopardy (Balcom & Pearce 2005). This mortality event seems to have a range of causes. Some appear to be environmentally related from factors such as eutrophication and an increase in the bottom temperature of the water, while others can be the result of intoxication from anthropogenic substances such as pesticides or even from the emergence of new pathogens such as Neoparamoeba pemaquidensis.(Moss et al. 2012). The complexity of the situation causing these high levels of morbidity for the Homarus Americanus of Long Island Sound is important to grasp in order to discover ways to nurse the population back to its flourishing, commercially significant self.​A factor that seemed to be the most prominent cause for the mortality event was the increase of the bottom water temperature of the sound. It is noted that Juvenile and Adult lobsters live in environments where the range in water temperature throughout the year is from 5[degrees]C to about 20[degrees]C. Temperature is also one the most dominant physiochemical parameters that effects the physiological properties of estuarine species with effects to the growth, rate of metabolic function, reproduction and overall health of species like homarus americanus. In 2005, it was discovered that as water temperature increased above 20.5[degrees]C the respiration rate of homarus americanus rapidly increased creating much stress amongst the lobster (Draxler et al. 2005). With historical records indicating the long-term temperatures of Long Island Sound are rising, it could be a devastating change for lobstermen along its shores, considering data has also showed an increase in water temperature is also linked to low bottom water dissolved oxygen levels. As lobsters in the Sound were seeking warmer water temperatures, they were also trying to avoid hypoxic areas, causing herding of lobsters in the western and central portions of the sound. When linking lobster abundance to the Sound temperature, data indicates a negative correlation between the average summer bottom water temperatures and the abundance of pre-recruit and recruit, male and female lobsters, from 1991 to 2003. Another negative link to increased water temperatures regards instances of dead lobster sightings with patterns indicating more deaths in the summers of 1999 and 2002 where the average temperatures were much higher than in 2000, 2001 and 2003 which had fewer deaths. Just like the annual data, monthly data also correlated higher temperatures with increased mortality. The months with the highest mortality had the highest bottom water temperatures which was often above 20[degrees]C (Benway et al. 2005). Other than an increase in respiratory rate and lower dissolved oxygen levels, an increase in water temperature can lead to the growth of natural populations of parasitic amoeba called Neoparamoeba pemaquidensis. This paramoeba was found effecting more than 90% of homarus americanus examined in late October of 1999 when the water temperatures were above average. Later that fall when the bottom water temperatures began to drop only about 29% of the lobster examined were infected by this paramoeba, thus creating a link between higher infection rates and higher temperatures (Balcolm & Pearce 2005). Other than Neoparamoeba pemaquidensis, many other bacteria and infections thrive in higher water temperatures. All of these factors indicate a very large correlation between the lobster mortality event of 1999 and the increase of water temperatures in Long Island Sound.​A concern of most lobstermen was the toxicity of the water. Many believed pollution from pesticides was a large factor in creating the 1999 mortality event of homarus americanus. The event corresponded in time with the application of various pesticides used to control the mosquito populations that were carrying West Nile virus. Sumithrin was the most prominent pesticide spread across New England. Lobstermen thought sumithrin might be linked to the paramoeba infecting the lobsters but studies indicated such pesticides degrade much too rapidly in water and does not exert a lethal level of toxicity (Brownawell et al. 2007).​Since the drastic mortality event in 1999 for homarus americanus living in Long Island Sound, there has been much research and studies put into determine a correct cause of death. The compiled data was able to point to an event mostly triggered by the rise in water temperature. The rise in temperatures not only directly affects the physiological characteristics of homarus americanus, but it can also have effects on environmental characteristics such as the dissolved oxygen levels of the water, and the growth of third-party factors that can affect the lobster population such as parasitic amoeba and other bacterias. The data was also able to rule out West Nile pesticides as a cause for the mortality event. If the numbers continue to follow the recent trend in regards to the temperature of the bottom water of Long Island Sound, we can expect to see a diminishing homarus americanus population.

Works Cited  - 

Benway, Burgess, Giannini, Hayden, Howell & Mckown. Oct. 2005. Long-term population trends in American lobster (Homarus americanus) and their relation to temperature in Long Island Sound. Journal of Shellfish Research. p.849 

 B. Brownawell, S. De Guise & M. Levin. Dec. 2007. Sumithrin immunotoxicity in the American Lobster (Homarus americanus) upon experimental exposure. Journal of Shellfish Research p.1162 

A.F Draxler, M.G. Lavigne, A.J. Paulson, R.M. Sherrell & D. Wieczorek. Oct. 2005. Manganese concentration in lobster (Homarus americanus) gills as an index of exposure to reducing conditions in western Long Island Sound. Journal of Shellfish Research. p815 

Nancy Balcolm & Jack Pearce. Oct. 2005. The 1999 Long Island Sound Lobster mortality event: findings of the comprehensive research initiative. Journal of Shellfish Research p691  

J.A. Moss, J.D. Shields & K.N. Wheeler. June 2012. Histological assessment of the lobster (Homarus americanus) in the “100 lobsters” project. Journal of Shellfish Research. p439