Complex sentence: During El Nino years, food supplies can drop extremely low, causing many seals to die from starvation, because El Niño raises the temperatures of the waters around the Galápagos, causing the seals food supply to migrate to cooler waters.
Split into simpler sentences: During El Nino years food supplies can drop extremely low, causing many seals to die from starvation. This is because El Nino raises the temperatures of the waters around the Galápagos, causing the seals food supply to migrate to cooler waters.